Methods and apparatuses for stabilizing the spine through an access device

ABSTRACT

An apparatus for stabilizing vertebrae while permitting a range of motion therebetween may include first and second fasteners for engaging adjacent vertebrae and a motion preserving device that can be coupled to the first and second fasteners. The motion preserving device may include a longitudinal member that includes an array of load-bearing elements. The longitudinal member may be configured to permit the load-bearing elements to move relative to each other and/or relative to other portions of the member. In some embodiments, the longitudinal member is relatively inflexible along a longitudinal axis and relatively flexible in a direction transverse to the longitudinal axis.

RELATED APPLICATION

This application is a continuation of U.S. patent application Ser. No.11/527,764, filed on Sep. 26, 2006, now U.S. Pat. No. 7,658,739, whichclaims the benefit under 35 U.S.C. §119(e) of U.S. Provisional PatentApplication No. 60/721,580, filed on Sep. 27, 2005, entitled “METHODSAND APPARATUSES FOR STABILIZING THE SPINE THROUGH AN ACCESS DEVICE,”which are hereby incorporated by reference herein in their entirety.

BACKGROUND OF THE DISCLOSURE

1. Field of the Disclosure

This application relates generally to methods and apparatuses forperforming minimally invasive surgery, and more particularly to methodsand apparatuses for performing procedures for stabilizing adjacent boneswhile preserving motion therebetween.

2. Description of the Related Art

In the past, patients suffering from degenerative spine conditions, suchas progressive degeneration of intervertebral discs, have been treatedby various techniques. For example, fixation and fusion are twoprocedures that are sometimes performed in combination to addressdegeneration of the intervertebral discs. Fusion involves thereplacement of an intervertebral disc with a bone graft intended to fusethe adjacent vertebrae together. Fixation provides an external structurethat bridges from one vertebra to an adjacent vertebra to eliminatemotion therebetween. While fusion and fixation may reduce some symptomsof disc degeneration, the elimination of motion reduces the patient'sflexibility and may cause other complications.

Also, these procedures are typically performed by way of open spinesurgery. In open spine surgery, the surgeon typically makes largeincisions and cuts or strips muscle tissue surrounding the spine toprovide open access to the troubled area. This technique exposes nervesin the open area, which can be injured when exposed. Consequently, opensurgery carries significant risks of scarring, pain, nerve damage, andblood loss. Open surgery also subjects patients to extended recoverytimes.

Less invasive techniques have been proposed to reduce the trauma of openspine surgery. For example, a constant diameter cannula has beenproposed to reduce incision length associated with open surgery.Unfortunately, such cannulae are usually very narrow and therefore theyprovide minimal space for the physician to observe the body structuresand manipulate surgical instruments.

SUMMARY OF THE DISCLOSURE

Accordingly, there is a need in the art for minimally invasive systemsand methods for stabilizing adjacent bone, e.g., vertebrae, whilepreserving motion therebetween. These systems and methods mayadvantageously provide a more normal post-recovery range of motion, andmay also limit stresses associated with other stabilization proceduresplaced on adjacent vertebrae and intervening discs.

One embodiment of the stabilization system comprises an apparatus forretaining a vertebrae of a spinal column in a desired spatialrelationship. The apparatus comprises a first fastener that has athreaded shank and an enlarged head. The threaded shank of the firstfastener engages a portion of a vertebra in use. The apparatus has afirst housing having a first passage and a second passage having alongitudinal axis extending transverse to the first passage. The firstfastener extends through an opening in the first housing into the secondpassage. The apparatus comprises a second fastener having a threadedshank and an enlarged head. The threaded shank of the second fastenerengages a portion of a vertebra in use. The apparatus has a secondhousing that has a first passage and a second passage having alongitudinal axis extending transverse to the first passage. The secondfastener extends through an opening in the second housing into thesecond passage. A longitudinal member having a first end and a secondend and comprising a plurality of thin sheets is configured to extendbetween the first and second housings. A first clamping device iscoupled with the first housing and is configured to secure the first endof the longitudinal member to the first housing. A second clampingdevice is coupled with the second housing and is configured to securethe second end of the longitudinal member to the second housing whileallowing the thin sheets to slide relative to each other and relative tothe second housing.

In another form, a method of stabilizing at least two vertebrae of thespine of a patient is provided. The method comprises coupling a firstscrew with a vertebra, the first screw having a first housing. A secondscrew having a second housing is coupled with another vertebra. A firstend of a multi-layered longitudinal member is secured with the firstscrew. A second end of the multi-layered longitudinal member is securedwith the second screw while allowing relative motion between the layersof the longitudinal member. In one variation, the first end is clampedwith the first screw, substantially preventing relative motion betweenthe layers of the longitudinal member at the first end.

In other techniques, a first cap screw is secured onto the first end ofthe longitudinal member to secure the longitudinal member in the firsthousing. A second cap screw is secured on the second end of thelongitudinal member to secure the second end of the longitudinal memberin the second housing while allowing relative motion between the secondend of the longitudinal member and the second housing. In someembodiments, the cap screw comprises a threaded portion configured toengage the housing and a yoke that is rotatably coupled with thethreaded portion and configured to engage the longitudinal member.

In another aspect, an apparatus for retaining vertebrae of a spinalcolumn in a desired spatial relationship is disclosed. The apparatuscomprises a first fastener having a threaded shank for engaging avertebral portion and a first housing having a first passage and asecond passage having a longitudinal axis extending transverse to thefirst passage. The first fastener extends through an opening in thehousing into the second passage. The apparatus also comprises a secondfastener having a threaded shank for engaging a vertebral portion and asecond housing having a first passage and a second passage having alongitudinal axis extending transverse to the first passage. The secondfastener extends through an opening in the housing into the secondpassage. The apparatus further comprises a longitudinal member having afirst end and a second end and a member axis extending therebetween. Thelongitudinal member comprises an array that comprises a plurality ofelongated load-bearing elements. The array may be configured to berelatively inflexible along the member axis but to be relativelyflexible in a direction transverse to the member axis. The array extendsat least partially between the first end and the second end of thelongitudinal member. The longitudinal member is configured to extendbetween the first passage of the first housing and the first passage ofthe second housing. The apparatus also comprises a first clamping deviceconfigured to be coupled with the first housing and to secure the firstend of the longitudinal member to the first housing, and a secondclamping device configured to be coupled with the second housing and tosecure the second end of the longitudinal member to the second housingwhile allowing the array of elongated elements to provide a range ofrelative movement of the vertebrae.

An embodiment of a longitudinal member is disclosed. The longitudinalmember has a first end and a second end and a member axis extendingtherebetween. The longitudinal member comprises an array that comprisesa plurality of elongated load-bearing elements. The array may beconfigured to be relatively inflexible along the member axis but to berelatively flexible in a direction transverse to the member axis. Thearray extends at least partially between the first end and the secondend of the longitudinal member. In some embodiments, the array comprisesa linear array or a cylindrical array. The elongated load bearingelements may include sheets, plates, rods, or a combination thereof.

An embodiment of a dynamic stabilization device for preserving a rangeof motion between adjacent vertebrae is provided. The dynamicstabilization device comprises a longitudinal member having a first endand a second end and a longitudinal axis extending therebetween. Thedynamic stabilization device further comprises an array that comprises aplurality of elongated load-bearing elements. The array is relativelyinflexible along the longitudinal axis and relatively flexible in adirection transverse to the longitudinal axis. The array extends atleast partially between the first end and the second end of thestabilization device, wherein in use the longitudinal member allows arange of relative movement of the vertebrae. An embodiment of anapparatus for retaining vertebrae of a spinal column in a desiredspatial relationship is disclosed. The apparatus comprises a firstfastener for engaging a first vertebra, a second fastener for engaging asecond vertebra, and an embodiment of the dynamic stabilization device,wherein in use the dynamic stabilization device is coupled to andextends between the first fastener and the second fastener.

In another form, an apparatus for retaining vertebrae of a spinal columnin a desired spatial relationship is disclosed. The apparatus comprisesa first fastener for engaging a portion of a vertebra and a secondfastener for engaging a portion of a vertebra. The apparatus alsocomprises a longitudinal member having a first end and a second end anda member axis extending therebetween. The longitudinal member comprisesan array that comprises a plurality of elongated load-bearing elements.The array may be configured to be relatively inflexible along the memberaxis but to be relatively flexible in a direction transverse to themember axis. The array extends at least partially between the first endand the second end of the longitudinal member. The longitudinal membermay be configured to extend between the first fastener and the secondfastener when engaged in the vertebrae and to allow a range of relativemovement of the vertebrae.

An embodiment of an apparatus for stabilizing vertebrae while permittinga range of motion therebetween may include first and second fastenersfor engaging adjacent vertebrae and a motion preserving device that maybe coupled to the first and second fasteners. The motion preservingdevice may include a longitudinal member that includes an array ofload-bearing elements. The longitudinal member may be configured topermit the load-bearing elements to move relative to each other and/orrelative to other portions of the member. In some embodiments, thelongitudinal member is relatively inflexible along a longitudinal axisand relatively flexible in a direction transverse to the longitudinalaxis.

In other embodiments, the longitudinal member comprises an array ofelongated elements. The elements may comprise different materials,including, for example, titanium, titanium alloys, or otherbiocompatible materials. In some embodiments, the longitudinal membercomprises a low friction material that is used to promote slidingbetween the elements (and/or between other portions of the longitudinalmember) and to reduce wear and to substantially prevent generation ofloose debris due to the relative motion within the member. A suitablelow-friction material includes ultra high molecular weight polyethylene(UHMWPE). In some embodiments, the longitudinal member includes layersthat alternate in composition, for example, in one embodiment the layersalternate between titanium and UHMWPE.

In some embodiments, one or both ends of the longitudinal member may besecured to the housings such that the layers may slide relative to eachother and relative to the housings. In other embodiments, one end of thelongitudinal member may be clamped to the housing such that motion ofthe layers relative to each other and relative to the housing isminimized. In such embodiments, the layers at one end of thelongitudinal member may be mechanically coupled together to preventtheir relative motion, for example, by the use of rivets, welds, oradhesives.

The spinal stabilization apparatus may comprise retention members thatlimit the longitudinal motion of an end of the longitudinal member whileallowing the elements to slide relative to each other and relative to atleast one of the retention members. In some embodiments, the retentionmembers may comprise a set of notches on the longitudinal member thatare mated to a set of notches on the housing or on the cap screw. Theset of notches may be disposed on one or more layers of the longitudinalmember.

By coupling the multi-layered longitudinal member to the vertebrae asdescribed, the longitudinal member acts as a spring that resistsextension and flexion of the vertebrae to which the stabilization deviceis coupled, thereby imparting stability and natural stiffness to adiseased or damaged portion of the spine. The characteristics of thespring such as its spring rate and stiffness may be chosen byappropriately selecting the number, the length and thickness, and thematerial properties of the layers. The spring rate may be linear ornonlinear. In some embodiments, the spring acts as a leaf spring. Insome embodiments, the longitudinal member acts as a spring in multipledimensions, for example, in two or more directions substantiallytransverse to a longitudinal axis of the member. In certain embodiments,the longitudinal member is relatively inflexible along the longitudinalaxis and/or is relatively flexible in directions transverse to thelongitudinal axis.

BRIEF DESCRIPTION OF THE DRAWINGS

Further objects, features and advantages of the disclosure will becomeapparent from the following detailed description taken in conjunctionwith the accompanying figures showing certain illustrative embodimentsof the disclosure, in which:

FIG. 1 is a perspective view of one embodiment of a surgical system andone embodiment of a method for treating the spine of a patient;

FIG. 2 is a perspective view of one embodiment of an expandable conduitin a reduced profile configuration;

FIG. 3 is a perspective view of the expandable conduit of FIG. 2 in afirst enlarged configuration;

FIG. 4 is a perspective view of the expandable conduit of FIG. 2 in asecond enlarged configuration;

FIG. 5 is a view of one embodiment of a skirt portion of an expandableconduit;

FIG. 6 is a view of another embodiment of a skirt portion of anexpandable conduit;

FIG. 7 is a perspective view of another embodiment of an expandableconduit in an enlarged configuration;

FIG. 8 is an enlarged sectional view of the expandable conduit of FIG. 7taken along lines 8-8 of FIG. 7;

FIG. 9 is a sectional view of the expandable conduit of FIG. 7 takenalong lines 9-9 of FIG. 7;

FIG. 10 is a perspective view of another embodiment of an expandableconduit in an enlarged configuration;

FIG. 11 is an enlarged sectional view of the expandable conduit of FIG.10 taken along lines 11-11 of FIG. 10;

FIG. 12 is a sectional view of the expandable conduit of FIG. 10 takenalong lines 12-12 of FIG. 10;

FIG. 13 is a view of a portion of another embodiment of the expandableconduit;

FIG. 14 is a view of a portion of another embodiment of the expandableconduit;

FIG. 15 is a sectional view illustrating one embodiment of a stage ofone embodiment of a method for treating the spine of a patient;

FIG. 16 is a side view of one embodiment of an expander apparatus in areduced profile configuration;

FIG. 17 is a side view of the expander apparatus of FIG. 16 in anexpanded configuration;

FIG. 18 is a sectional view of the expander apparatus of FIGS. 16-17inserted into the expandable conduit of FIG. 2, which has been insertedinto a patient;

FIG. 19 is a sectional view of the expander apparatus of FIGS. 16-17inserted into the expandable conduit of FIG. 2 and expanded to theexpanded configuration to retract tissue;

FIG. 20 is an exploded perspective view of one embodiment of anendoscope mount platform;

FIG. 21 is a top view of the endoscope mount platform of FIG. 20 coupledwith one embodiment of an indexing arm and one embodiment of anendoscope;

FIG. 22 is a side view of the endoscope mount platform of FIG. 20illustrated with one embodiment of an indexing arm and one embodiment ofan endoscope;

FIG. 23 is a perspective view of one embodiment of an indexing collar ofthe endoscope mount platform FIG. 20;

FIG. 24 is a perspective view of one embodiment of an endoscope;

FIG. 25 is a partial sectional view of one embodiment of a stage of oneembodiment of a method for treating the spine of a patient;

FIG. 26 is a perspective view of one embodiment of a fastener;

FIG. 27 is an exploded perspective view of the fastener of FIG. 26;

FIG. 27( a) is an enlarged side view of one embodiment of a biasingmember illustrated in FIG. 27 taken from the perspective of the arrow 27a;

FIG. 28 is a perspective view of one embodiment of a surgicalinstrument;

FIG. 29 is an enlarged sectional view of the fastener of FIGS. 26-27coupled with the surgical instrument of FIG. 28, illustrating oneembodiment of a stage of one embodiment of a method for treating thespine of a patient;

FIG. 30 is side view of one embodiment of another surgical instrument;

FIG. 31 is a partial sectional view of one embodiment of a stage of oneembodiment of a method for treating the spine of a patient;

FIG. 32 is a side view of one embodiment of another surgical instrument;

FIG. 33 is a perspective view similar to FIG. 31 illustrating theapparatuses of FIGS. 26 and 32, in one embodiment of a stage of oneembodiment of a method for treating the spine of a patient;

FIG. 34 is an enlarged sectional view of the apparatus of FIGS. 26 and32, illustrating one embodiment of a stage of one embodiment of a methodfor treating the spine of a patient;

FIG. 35 is an enlarged sectional similar to FIG. 34, illustrating oneembodiment of a stage of one embodiment of a method for treating thespine of a patient;

FIG. 36 is an enlarged view in partial section illustrating oneembodiment of a stage of one embodiment of a method for treating thespine of a patient;

FIG. 37 is a partial view illustrating one embodiment of a stage of oneembodiment of a method for treating the spine of a patient;

FIG. 38 is a schematic view of one embodiment of a dynamic stabilizationdevice shown applied to a spine of a patient;

FIG. 39 is a partial cross-sectional view of a portion of the dynamicstabilization device of FIG. 38;

FIG. 40 is a detail view of a portion of the dynamic stabilizationdevice of FIG. 38;

FIG. 41 is an elevation view illustrating one embodiment of a dynamicstabilization device applied to a human spine;

FIG. 42 is a lateral elevation view illustrating one embodiment of adynamic stabilization device applied to a human spine;

FIG. 43 is a detail view illustrating one embodiment of a dynamicstabilization device;

FIG. 44 is a perspective view illustrating one embodiment of a dynamicstabilization device applied to a human spine;

FIG. 45 is a perspective view illustrating one embodiment of a dynamicstabilization device or stabilization system having a longitudinalmember comprising a plurality of thin sheets;

FIG. 46 is an exploded perspective view of the longitudinal member andclamping devices of the dynamic stabilization device of FIG. 45;

FIG. 46A is perspective view of another embodiment of a longitudinalmember;

FIG. 46B is a perspective view of another embodiment of a dynamicstabilization apparatus;

FIG. 46C is a side plan view of the dynamic stabilization apparatus ofFIG. 46B;

FIG. 46D is a top plan view of the dynamic stabilization apparatus ofFIG. 46B;

FIG. 46E is a side cross-section view of the dynamic stabilizationapparatus taken along section plane 46E-46E of FIG. 46D;

FIG. 46F is an exploded perspective view illustrating one embodiment ofa longitudinal member;

FIG. 46G is a perspective view of the longitudinal member of FIG. 46F,with an optional sheath removed for clarity of illustration;

FIG. 46H is a perspective view of another embodiment of a longitudinalmember;

FIG. 46I is a perspective view of another embodiment of a longitudinalmember;

FIG. 46J is a perspective view of another embodiment of a longitudinalmember;

FIG. 47 is a plan view of the dynamic stabilization device of FIG. 45;

FIG. 48 is an end view of the dynamic stabilization device of FIG. 45;

FIG. 49 is a partial cross-section view of the dynamic stabilizationdevice of FIG. 48 taken along section plane 49-49;

FIG. 50 is a plan view of the dynamic stabilization device of FIG. 47 ina configuration corresponding to extension of the spine;

FIG. 51 is an end view of the dynamic stabilization device of FIG. 47 inthe configuration of FIG. 50;

FIG. 52 is a partial cross-section view of the dynamic stabilizationdevice of FIG. 51 taken along section plane 52-52;

FIG. 53 is an end view of the dynamic stabilization device of FIG. 47 ina configuration corresponding to flexion of the spine;

FIG. 54 is a partial cross-section view of the dynamic stabilizationdevice of FIG. 53 taken along section plane 54-54;

FIG. 55 is an elevation view illustrating one embodiment of a dynamicstabilization device applied to a human spine;

FIG. 56 is a schematic view of one embodiment of an access deviceapplied through the skin of a patient to provide access to a surgicallocation near the spine in connection with a dynamic stabilizationprocedure;

FIG. 57 is a lateral view of two adjacent vertebrae of the spine towhich the access device of FIG. 56 has been applied, illustrating theapplication of one embodiment of a dynamic stabilizer;

FIG. 58 is a lateral view of two adjacent vertebrae of the spine towhich the access device of FIG. 56 has been applied, illustrating theapplication of another embodiment of a dynamic stabilizer; and

FIG. 59 is a lateral view of two adjacent vertebrae of the spine towhich the access device of FIG. 56 has been applied, illustrating theapplication of another embodiment of a dynamic stabilizer.

Throughout the figures, the same reference numerals and characters,unless otherwise stated, are used to denote like features, elements,components or portions of the illustrated embodiments. Moreover, whilethe subject matter of the disclosure will now be described in detailwith reference to the figures, it is done so in connection with theillustrative embodiments. It is intended that changes and modificationscan be made to the described embodiments without departing from the truescope and spirit of the subject invention as defined by the appendedclaims.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

As should be understood in view of the following detailed description,this application is directed to apparatuses and methods for treating thespine of a patient through an access device, also referred to herein asan expandable conduit. More particularly, the systems described belowprovide access to surgical locations at or near the spine and provide avariety of tools and implants or implantable devices useful inperforming treatment of the spine. For example, systems and methods aredescribed herein that may be used to provide motion preservingstabilization of the spine, such as dynamic stabilization. Accessdevices and systems described herein enable these systems and methods tobe practiced minimally invasively. Also, the systems described hereinenable a surgeon to perform a wide variety of methods as describedherein.

I. Systems for Performing Procedures at a Surgical Location

Various embodiments of apparatuses and procedures described herein willbe discussed in terms minimally invasive procedures and apparatuses,e.g., of endoscopic apparatuses and procedures. Many aspects of thepresent disclosure may also find use in conventional, open, andmini-open procedures. In the drawings and description which follows, theterm “proximal,” as is traditional, refers to the end portion of theapparatus which is closest to the operator, while the term “distal” willrefer to the end portion which is farthest from the operator.

FIG. 1 shows one embodiment of a surgical system 10 that can be used toperform a variety of methods or procedures. In at least a portion of theprocedure, as discussed more fully below, the patient P can be placed inthe prone position on operating table T, taking care that the abdomen isnot compressed and physiological lordosis is preserved, as is known inthe art. The physician D is able to access the surgical site and performthe surgical procedure with the components of the system 10, which willbe described in greater detail herein. The system 10 may be supported,in part, by a mechanical support arm A, such as the type generallydisclosed in U.S. Pat. No. 4,863,133, which is hereby incorporated byreference herein in its entirety. One mechanical arm of this type ismanufactured by Leonard Medical, Inc., 1464 Holcomb Road, HuntingtonValley, Pa., 19006.

Visualization of the surgical site may be achieved in any suitablemanner, e.g., by use of a viewing element, such as an endoscope, acamera, loupes, a microscope, direct visualization, or any othersuitable viewing element, or a combination of the foregoing. In oneembodiment, the viewing element provides a video signal representingimages, such as images of the surgical site, to a monitor M. The viewingelement may be an endoscope and camera which captures images to bedisplayed on the monitor M whereby the physician D is able to view thesurgical site as the procedure is being performed. The endoscope andcamera will be described in greater detail herein.

The systems and procedures will be described herein in connection withminimally invasive postero-lateral spinal surgery. One such method is atwo level postero-lateral fixation of the spine involving the L4, L5,and S1 vertebrae. (In the drawings, the vertebrae will generally bedenoted by reference letter V.) The usefulness of the apparatuses andprocedures is neither restricted to the postero-lateral approach nor tothe L4, L5, and S1 vertebrae, but it may be used in other anatomicalapproaches and other vertebra(e) within the cervical, thoracic, andlumbar regions of the spine. The procedures may be directed towardsurgery involving one or more vertebral levels. It is also useful foranterior and lateral procedures. Moreover, it is believed that manyembodiments may be also particularly useful where any body structuresmust be accessed beneath the skin and muscle tissue of the patient, andwhere it desirable to provide sufficient space and visibility in orderto manipulate surgical instruments and treat the underlying bodystructures. For example, certain features or instrumentation describedherein are particularly useful for a minimally invasive procedures,e.g., arthroscopic procedures. As discussed more fully below, oneembodiment of an apparatus described herein provides an expandableconduit that has an expandable distal portion. The expandable distalportion prevents or substantially prevents the expandable conduit orinstruments extended therethrough to the surgical site from beingdislodging or popping out of the operative site.

The system 10 includes an expandable conduit or access device thatprovides a internal passage for surgical instruments to be insertedthrough the skin and muscle tissue of the patient P to the surgicalsite. The expandable conduit has a wall portion defining reduced profileconfiguration for initial percutaneous insertion into the patient. Thiswall portion may have any suitable arrangement. In one embodiment,discussed in more detail below, the wall portion has a generally tubularconfiguration that may be passed over a dilator that has been insertedinto the patient to atraumatically enlarge an opening sufficiently largeto receive the expandable conduit therein.

The wall portion of the expandable conduit is subsequently expanded toan enlarged configuration, by moving against the surrounding muscletissue to at least partially define an enlarged surgical space in whichthe surgical procedures will be performed. In a sense, it acts as itsown dilator. The expandable conduit may also be thought of as aretractor, and may be referred to herein as such. The distal portion canbe expanded to a greater extent than the proximal portion, because thesurgical procedures are to be performed at the surgical site which isadjacent the distal portion when the expandable conduit is inserted intothe patient.

While in the reduced profile configuration, the expandable conduitdefines a first unexpanded configuration. Thereafter, the expandableconduit enlarges the surgical space defined thereby by engaging thetissue surrounding the conduit and displacing the tissue radiallyoutwardly as the conduit expands. The expandable conduit may besufficiently rigid to displace such tissue during the expansion thereof.The expandable conduit may be resiliently biased to expand from thereduced profile configuration to the enlarged configuration. Inaddition, the conduit may also be manually expanded by an expanderdevice with or without one or more surgical instruments insertedtherein, as will be described below. The surgical site is at leastpartially defined by the expanded conduit itself. During expansion, theconduit moves from the first overlapping configuration to a secondoverlapping configuration.

In addition to enlargement, the distal end portion of the expandableconduit may be configured for relative movement with respect to theproximal end portion in order to allow the physician to preciselyposition the distal end portion at the desired location. This relativemovement also provides the advantage that the proximal portion of theexpandable conduit nearest the physician D may remain substantiallystable during such distal movement. In an exemplary embodiment, thedistal portion is a separate component which is pivotably or movablyattached relative to the proximal portion. In another embodiment, thedistal portion is flexible or resilient in order to permit such relativemovement.

One embodiment of an expandable conduit is illustrated in FIGS. 2-6 anddesignated by reference number 20. The expandable conduit 20 includes aproximal wall portion 22, which has a tubular configuration, and adistal wall portion, which is an expandable skirt portion 24. The skirtportion 24 is enlargeable from a reduced profile configuration having aninitial dimension 26 and corresponding cross-sectional area (illustratedin FIG. 2), to an enlarged configuration having a dimension 28 andcorresponding cross-sectional area (illustrated in FIG. 4). In oneembodiment, the skirt portion 24 is attached to the proximal wallportion 22 with a rivet 30, pin, or similar connecting device to permitmovement of the skirt portion 24 relative to the proximal wall portion22.

In the illustrated embodiment, the skirt portion 24 is manufactured froma resilient material, such as stainless steel. The skirt portion 24 ismanufactured so that it normally assumes an expanded configurationillustrated in FIG. 4. As illustrated in FIG. 3, the skirt portion 24may assume an intermediate dimension 34 and correspondingcross-sectional area, which is greater than the dimension 26 of thereduced profile configuration of FIG. 2, and smaller than the dimension28 of the enlarged configuration of FIG. 4. The skirt portion 24 mayassume the intermediate configuration of FIG. 3 when deployed in thepatient in response to the force of the tissue acting on the skirtportion 24. The intermediate dimension 34 will depend upon severalfactors, including the rigidity of the skirt portion 24, the surroundingtissue, and whether such surrounding tissue has relaxed or tightenedduring the course of the procedure. An outer plastic sleeve 32(illustrated in dashed line in FIG. 2) may be provided which surroundsthe expandable conduit 20 and maintains the skirt portion 24 in thereduced profile configuration. The outer sleeve 32 may have a braidedpolyester suture embedded within it (not shown), aligned substantiallyalong the longitudinal axis thereof; such that when the suture iswithdrawn, the outer sleeve 32 is torn, which allows the expandableconduit 20 to resiliently expand from the reduced profile configurationof FIG. 2 to the expanded configurations of FIGS. 3-4. While in thereduced profile configuration of FIG. 2, the skirt portion 24 defines afirst overlapping configuration 33, as illustrated by the dashed line.As the skirt portion 24 resiliently expands, the skirt portion 24assumes the expanded configuration, as illustrated in FIGS. 3-4.

The skirt portion 24 is sufficiently rigid that it is capable ofdisplacing the tissue surrounding the skirt portion 24 as it expands.Depending upon the resistance exerted by surrounding tissue, the skirtportion is sufficiently rigid to provide some resistance against thetissue to remain in the configurations of FIGS. 3-4. Moreover, theexpanded configuration of the skirt portion 24 is at least partiallysupported by the body tissue of the patient. The rigidity of the skirtportion 24 and the greater expansion at the distal portion creates astable configuration that is at least temporarily stationary in thepatient, which frees the physician from the need to actively support theconduit 20 until an endoscope mount platform 300 and a support arm 400are subsequently added in one embodiment (see FIGS. 21-22).

The skirt portion 24 of the expandable conduit 20 is illustrated in aninitial flattened configuration in FIG. 5. The skirt portion 24 may bemanufactured from a sheet of stainless steel having a thickness of about0.007 inches. In various embodiments, the dimension 28 of the skirtportion 24 is about equal to or greater than 50 mm, is about equal to orgreater than 60 mm, is about equal to or greater than 70 mm, is aboutequal to or greater than 80 mm, or is any other suitable size, when theskirt portion 24 is in the enlarged configuration. In one embodiment,the dimension 28 is about 63 mm, when the skirt portion 24 is in theenlarged configuration. As discussed above, the unrestricted shape ofthe skirt portion 24 preferably is a circular or an oblong shape. Theskirt portion 24 may also take on an oval shape, wherein the dimension28 would define a longer dimension the skirt portion 24 and would beabout 85 mm in one embodiment. In another embodiment, the skirt portion24 has an oval shape and the dimension 28 defines a longer dimension ofthe skirt portion 24 and would be about 63 mm. An increased thickness,e.g., about 0.010 inches, may be used in connection with skirt portionshaving a larger diameter, such as about 65 mm. Other materials, such asnitinol or plastics having similar properties, may also be useful.

As discussed above, the skirt portion 24 is attached to the proximalwall portion 22 with a pivotable connection, such as rivet 30. A pair ofrivet holes 36 is provided in the skirt portion 24 to receive the rivet30. The skirt portion 24 also has two free ends 38 and 40 in oneembodiment that are secured by a slidable connection, such as secondrivet 44 (not shown in FIG. 5, illustrated in FIGS. 2-4). A pair ofcomplementary slots 46 and 48 is defined in the skirt portion 24adjacent the free ends 38 and 40. The rivet 44 is permitted to movefreely within the slots 46 and 48. This slot and rivet configurationallows the skirt portion 24 to move between the reduced profileconfiguration of FIG. 2 and the enlarged or expanded configurations ofFIGS. 3-4. The use of a pair of slots 46 and 48 reduces the risk of the“button-holing” of the rivet 44, e.g., a situation in which the openingof the slot becomes distorted and enlarged such that the rivet may slideout of the slot, and cause failure of the device. However, thelikelihood of such occurrence is reduced in skirt portion 24 becauseeach of the slots 46 and 48 in the double slot configuration has arelatively shorter length than a single slot configuration. Beingshorter, the slots 46, 48 are less likely to be distorted to the extentthat a rivet may slide out of position. In addition, the configurationof rivet 44 and slots 46 and 48 permits a smoother operation ofenlarging and reducing the skirt portion 24, and allows the skirtportion 24 to expand to span as many as three vertebrae, e.g., L4, L5,and SI, to perform multi-level fixation alone or in combination with avariety of other procedures, as discussed below.

An additional feature of the skirt portion 24 is the provision of ashallow concave profile 50 defined along the distal edge of the skirtportion 24, which allows for improved placement of the skirt portion 24with respect to the body structures and the surgical instruments definedherein. In one embodiment, a pair of small scalloped or notched portions56 and 58 is provided, as illustrated in FIG. 5. When the skirt portion24 is assembled, the notched portions 56 and 58 are oriented in thecephcaudal direction (indicated by an arrow 60 in FIG. 4) and permitinstrumentation, such as an elongated member 650 used in a fixationprocedure (described in detail below), to extend beyond the areaenclosed by the skirt portion 24 without moving or raising the skirtportion 24 from its location to allow the elongated member 650 to passunder the skirt portion 24. The notched portions 56, 58 are optional, asillustrated in connection with another embodiment of an expandableconduit 54, illustrated in FIG. 6, and may be eliminated where thephysician deems the notches to be unnecessary for the procedures to beperformed, (e.g., where fixation does not require extended access, asdiscussed more fully below.)

As illustrated in FIG. 4, the skirt portion 24 may be expanded to asubstantially conical configuration having a substantially circular orelliptical profile. In another embodiment, features may be provided onthe skirt portion which facilitate the bending of the skirt portion atseveral locations to provide a pre-formed enlarged configuration. Forexample, another embodiment of an expandable conduit 70, illustrated inFIGS. 7-9, provides a skirt portion 74 that has four sections 76 a, 76b, 76 c, 76 d having a reduced thickness. For a skirt portion 74 havinga thickness 78 of about 0.007 inches, reduced thickness sections 76 a,76 b, 76 c, 76 d may have a thickness 80 of about 0.002-0.004 inches(FIG. 8). The reduced thickness sections 76 a, 76 b, 76 c, 76 d may havea width 82 of about 1-5 mm. The thickness 78 of the skirt portion 74 maybe reduced by milling or grinding, as is known in the art. When theskirt portion 74 is opened, it moves toward a substantially rectangularconfiguration, as shown in FIG. 9, subject to the resisting forces ofthe body tissue. In another embodiment (not shown), a skirt portion maybe provided with two reduced thickness sections (rather than the fourreduced thickness sections of skirt 74) which would produce asubstantially “football”-shaped access area.

FIGS. 10-12 show another embodiment of an expandable conduit 80. Theexpandable conduit 80 has a skirt portion 84 with a plurality ofperforations 86. The perforations 86 advantageously increase theflexibility at selected locations. The size and number of perforations86 may vary depending upon the desired flexibility and durability. Inanother embodiment, the skirt portion 84 may be scored or otherwiseprovided with a groove or rib in order to facilitate the bending of theskirt portion at the desired location.

FIG. 13 illustrates another embodiment of an expandable conduit that hasa skirt portion 94 having one slot 96 and an aperture 98. A rivet (notshown) is stationary with respect to the aperture 98 and slides withinthe slot 96. FIG. 14 illustrates another embodiment of an expandableconduit that has a skirt portion 104 that includes an aperture 108. Theapertures 108 receives a rivet (not shown) that slides within elongatedslot 106.

Further details of the expandable conduit are described in U.S. Pat. No.6,187,000, and in U.S. patent application Ser. No. 09/772,605, filedJan. 30, 2001, U.S. application Ser. No. 10/361,887 filed Feb. 10, 2003,and application Ser. No. 10/280,489 filed Oct. 25, 2002, which areincorporated by reference in their entirety herein.

In one embodiment of a procedure, an early stage involves determining apoint in the skin of the patient at which to insert the expandableconduit. The access point preferably corresponds to theposterior-lateral aspects of the spine. Manual palpation andAnterior-Posterior (AP) fluoroscopy may be used to determine preferredor optimal locations for forming an incision in the skin of the patient.In one embodiment, the expandable conduit 20 preferably is placed midway(in the cephcaudal direction) between the L4 through SI vertebrae,centrally about 4-7 cm from the midline of the spine.

After the above-described location is determined, an incision is made atthe location. A guide wire (not shown) is introduced under fluoroscopicguidance through the skin, fascia, and muscle to the approximatesurgical site. A series of dilators is used to sequentially expand theincision to the desired width, about 23 mm in one procedure, withoutdamaging the structure of surrounding tissue and muscles. A firstdilator is placed over the guide wire, which expands the opening. Theguide wire is then subsequently removed. A second dilator that isslightly larger than the first dilator is placed over the first dilator,which expands the opening further. Once the second dilator is in place,the first dilator is subsequently removed. This process of (1)introducing a next-larger-sized dilator coaxially over the previousdilator and (2) subsequently removing the previous dilator when thenext-larger-sized dilator is in place continues until an opening of thedesired size is created in the skin, muscle, and subcutaneous tissue. Inone embodiment of the method, desired opening size is about 23 mm.(Other dimensions of the opening, e.g., about 20 mm, 27 mm, 30 mm, etc.,are also useful with this apparatus in connection with spinal surgery,and still other dimensions are contemplated.)

FIG. 15 shows that following placement of a dilator 120, which is thelargest dilator in the above-described dilation process, the expandableconduit 20 is introduced in its reduced profile configuration andpositioned in a surrounding relationship over the dilator 120. Thedilator 120 is subsequently removed from the patient, and the expandableconduit 20 is allowed to remain in position.

Once positioned in the patient, the expandable conduit 20 may beenlarged to provide a passage for the insertion of various surgicalinstruments and to provide an enlarged space for performing theprocedures described herein. As described above, the expandable conduitmay achieve the enlargement in several ways. In one embodiment, a distalportion of the conduit may be enlarged, and a proximal portion maymaintain a constant diameter. The relative lengths of the proximalportion 22 and the skirt portion 24 may be adjusted to vary the overallexpansion of the conduit 20. Alternatively, such expansion may extendalong the entire length of the expandable conduit 20. In one embodimentof a procedure, the expandable conduit 20 may be expanded by removing asuture 35 and tearing the outer sleeve 32 surrounding the expandableconduit 20, and subsequently allowing the skirt portion 24 toresiliently expand towards its fully expanded configuration as(illustrated in FIG. 4) to create an enlarged surgical space from the L4to the SI vertebrae. The resisting force exerted on the skirt portion 24may result in the skirt portion 24 assuming the intermediateconfiguration illustrated in FIG. 3. Under many circumstances, the spacecreated by the skirt portion 24 in the intermediate configuration is asufficiently large working space to perform the procedure describedherein. Once the skirt portion 24 has expanded, the rigidity andresilient characteristics of the skirt portion 24 allow the expandableconduit 20 to resist closing to the reduced profile configuration ofFIG. 2 and to at least temporarily resist being expelled from theincision. These characteristics create a stable configuration for theconduit 20 to remain in position in the body, supported by thesurrounding tissue. It is understood that additional support may beneeded, especially if an endoscope is added.

According to one embodiment of a procedures, the expandable conduit 20may be further enlarged at the skirt portion 24 using an expanderapparatus to create a surgical access space. An expander apparatususeful for enlarging the expandable conduit has a reduced profileconfiguration and an enlarged configuration. The expander apparatus isinserted into the expandable conduit in the reduced profileconfiguration, and subsequently expanded to the enlarged configuration.The expansion of the expander apparatus also causes the expandableconduit to be expanded to the enlarged configuration. In someembodiments, the expander apparatus may increase the diameter of theexpandable conduit along substantially its entire length in a conicalconfiguration. In other embodiments, the expander apparatus expands onlya distal portion of the expandable conduit, allowing a proximal portionto maintain a constant diameter.

In addition to expanding the expandable conduit, the expander apparatusmay also be used to position the distal portion of the expandableconduit at the desired location for the surgical procedure. The expanderengages an interior wall of the expandable conduit, and moves theconduit to the proper location. For the embodiments in which the distalportion of the expandable conduit is relatively movable with respect tothe proximal portion, the expander apparatus is useful to position thedistal portion without substantially disturbing the proximal portion.

In some procedures, an expander apparatus is used to further expand theskirt portion 24 towards the enlarged configuration (illustrated in FIG.4). The expander apparatus is inserted into the expandable conduit, andcan have two or more members which are movable to engage the interiorwall of the skirt portion 24 and apply a force sufficient to furtherexpand the skirt portion 24. FIGS. 16 and 17 show one embodiment of anexpander apparatus 200 that has a first component 202 and a secondcomponent 204. A first component 202 and a second component 204 of theexpander apparatus 200 are arranged in a tongs-like configuration andare pivotable about a pin 206. The first and second components 202 and204 can be constructed of steel having a thickness of about 9.7 min.Each of the first and second components 202 and 204 has a proximalhandle portion 208 and a distal expander portion 210. Each proximalhandle portion 208 has a finger grip 212 that may extend transverselyfrom an axis, e.g., a longitudinal axis 214, of the apparatus 200. Theproximal handle portion 208 may further include a stop element, such asflange 216 that extends transversely from the longitudinal axis 214. Theflange 216 is dimensioned to engage the proximal end 25 of theexpandable conduit 20 when the apparatus 200 is inserted a predetermineddepth. This arrangement provides a visual and tactile indication of theproper depth for inserting the expander apparatus 200. In oneembodiment, a dimension 218 from the flange 216 to the distal tip 220 isabout 106 mm. The dimension 218 is determined by the typical depth ofthe body structures beneath the skin surface at which the surgicalprocedure is being performed. The distal portions 210 are each providedwith an outer surface 222 for engaging the inside wall of the skirtportion 24. The outer surface 222 is a frusto-conical surface in oneembodiment. The expander apparatus 200 has an unexpanded distal width224 at the distal tip 220 that is about 18.5 mm in one embodiment.

In use, the finger grips 212 are approximated towards one another, asindicated by an arrow A in FIG. 17, which causes the distal portions 210to move to the enlarged configuration, as indicated by arrows B. Thecomponents 202 and 204 are also provided with a cooperating tab 226 andshoulder portion 228 which are configured for “mutual engagement whenthe distal portions 210 are in the expanded configuration. In theillustrated embodiment, the expander apparatus 200 has an expandeddistal width 230 that extends between the distal portions 210. Theexpanded distal width 230 can be about 65 mm or less, about as large as83 mm or less, or any other suitable width. The tab 226 and shoulderportion 228 together limit the expansion of the expander apparatus 200to prevent expansion of the skirt portion 24 of the expandable conduit20 beyond its designed dimension, and to minimize trauma to theunderlying tissue. Further details of the expander apparatus aredescribed in U.S. patent application Ser. No. 09/906,463 filed Jul. 16,2001, which is incorporated by reference in their entirety herein.

When the expandable conduit 20 is inserted into the patient and theouter sleeve 32 is removed, the skirt portion 24 expands to a pointwhere the outward resilient expansion of the skirt portion 24 isbalanced by the force of the surrounding tissue. The surgical spacedefined by the conduit may be sufficient to perform any of a number ofsurgical procedures or combination of surgical procedures describedherein. However, if it is desired to expand the expandable conduit 20further, the expander apparatus 200 may be inserted into the expandableconduit 20 in the reduced profile configuration until the shoulderportions 216 are in approximation with the proximal end 25 of the skirtportion 24 of the expandable conduit 20, as shown in FIG. 18.

FIG. 18 shows the expander apparatus 200 is inserted in the expandableconduit 20 in the reduced profiled configuration. Expansion of theexpander apparatus 200 is achieved by approximating the handle portions212 (not shown in FIG. 18), which causes the distal portions 210 of theexpander apparatus 200 to move to a spaced apart configuration. As thedistal portions 210 move apart and contact the inner wall of the skirtportion 24, the skirt portion 24 is expanded by allowing the rivet 44 toslide within the slots 46 and 48 of the skirt portion 24. When thedistal portions 210 reach the maximum expansion of the skirt portion 24(illustrated by a dashed line in FIG. 19), the tab 226 and shoulderportion 228 of the expander apparatus 200 come into engagement toprevent further expansion of the tong portions (as illustrated in FIG.17). The conduit 20 may be alternatively further expanded with a balloonor similar device.

A subsequent, optional step in the procedure is to adjust the locationof the distal portion of the expandable conduit 20 relative to the bodystructures to be operated on. For example, the expander apparatus 200may also be used to engage the inner wall of the skirt portion 24 of theexpandable conduit 20 in order to move the skirt portion 24 of theexpandable conduit 20 to the desired location. For an embodiment inwhich the skirt portion 24 of the expandable conduit 20 is relativelymovable relative to the proximal portion, e.g. by use of the rivet 30,the expander apparatus 200 is useful to position the skirt portion 24without substantially disturbing the proximal portion 22 or the tissuescloser to the skin surface of the patient. As will be described below,the ability to move the distal end portion, e.g., the skirt portion 24,without disturbing the proximal portion is especially beneficial when anadditional apparatus is mounted relative to the proximal portion of theexpandable conduit, as described below.

An endoscope mount platform 300 and indexing arm 400 provide securementof an endoscope 500 on the proximal end 25 of the expandable conduit 20for remotely viewing the surgical procedure, as illustrated in FIGS.20-23. The endoscope mount platform 300 may also provide several otherfunctions during the surgical procedure. The endoscope mount platform300 includes a base 302 that extends laterally from a central opening304 in a general ring-shaped configuration. The base 302 provides an aidfor the physician, who is primarily viewing the procedure by observing amonitor, when inserting surgical instruments into the central opening304. For example, the size of the base 302 provides visual assistance(as it may be observable in the physician's peripheral vision) as wellas provides tactile feedback as the instruments are lowered towards thecentral opening 304 and into the expandable conduit 20.

The endoscope mount platform 300 further provides a guide portion 306that extends substantially parallel to a longitudinal axis 308 away fromthe central opening 304. The base 302 can be molded as one piece withthe guide portion 306. The base 302 and guide portion 306 may beconstructed as a suitable polymer such as polyetheretherketone (PEEK).

The guide portion 306 includes a first upright member 310 that extendsupward from the base 302 and a second upright member 312 that extendsupward from the base 302. The upright members 310, 312 each have arespective vertical grooves 314 and 315 that can slidably receive anendoscopic mount assembly 318.

The endoscope 500 (not shown in FIG. 20) is movably mounted to theendoscope mount platform 300 by the endoscope mount assembly 318. Theendoscope mount assembly 318 includes an endoscope mount 320 and asaddle unit 322. The saddle unit 322 is slidably mounted is within thegrooves 314 and 315 in the upright members 310 and 312. The endoscopemount 320 receives the endoscope 500 through a bore 326 which passesthrough the endoscope mount 320. Part of the endoscope 500 may extendthrough the expandable conduit 20 substantially parallel to longitudinalaxis 308 into the patient's body 130.

The endoscope mount 320 is removably positioned in a recess 328 definedin the substantially “U”-shaped saddle unit 322, which is selectivelymovable in a direction parallel to the longitudinal axis 308 in order toposition the endoscope 500 at the desired height within the expandableconduit 20 to provide a zoom feature to physician's view of the surgicalprocedure.

A screw mechanism 340 is positioned on the base 302 between the uprightmembers 310 and 312, and is used to selectively move the saddle unit322, and the endoscope mount 320 and the endoscope 500 which aresupported by the saddle unit 322. The screw mechanism 340 comprises athumb wheel 342 and a spindle 344. The thumb wheel 343 is rotatablymounted in a bore in the base 302. The thumb wheel 342 has an externalthread 346 received in a cooperating thread in the base 302. The spindle344 is mounted for movement substantially parallel to the central axis308. The spindle 344 has a first end received in a rectangular openingin the saddle unit 322, which inhibits rotational movement of thespindle 344. The second end of the spindle 344 has an external threadwhich cooperates with an internal thread formed in a bore within thethumb wheel 342. Rotation of the thumb wheel 342 relative to the spindle344, causes relative axial movement of the spindle unit 344 along withthe saddle unit 322. Further details of the endoscope mount platform aredescribed in U.S. patent application Ser. No. 09/491,808 filed Jan. 28,2000, application Ser. No. 09/821,297 filed Mar. 29, 2001, andapplication Ser. No. 09/940,402 filed Aug. 27, 2001.

FIG. 21-23 show that the endoscope mount platform 300 is mountable tothe support arm 400 in one embodiment. The support arm 400, in turn,preferably is mountable to mechanical support, such as mechanicalsupport arm A, discussed above in connection with FIG. 1. The supportarm 400 rests on the proximal end 25 of the expandable conduit 20. Thesupport arm 400 includes an indexing collar 420, which is received inthe central opening 304 of the base 302 of endoscope mount platform 300.The indexing collar 420 is substantially toroidal in section and has anouter peripheral wall surface 422, an inner wall surface 424, and a wallthickness 426 that is the distance between the wall surfaces 422, 424.The indexing collar 420 further includes a flange 428, which supportsthe indexing collar 420 on the support arm 400.

The collars 420 advantageously make the surgical system 10 a modular inthat different expandable conduits 20 may be used with a singleendoscope mount platform 300. For example, expandable conduits 20 ofdifferent dimensions may be supported by providing of indexing collars420 to accommodate each conduit size while using a single endoscopemount platform 300. The central opening 304 of the endoscope mountplatform 300 has constant dimension, e.g., a diameter of about 32.6 mm.An appropriate indexing collar 420 is selected, e.g., one that isappropriately sized to support a selected expandable conduit 20. Thusthe outer wall 422 and the outer diameter 430 are unchanged betweendifferent indexing collars 420, although the inner wall 424 and theinner diameter 432 vary to accommodate differently sized conduits 20.

The indexing collar 420 is mounted to the proximal portion of theexpandable conduit 20 and allows angular movement of the endoscope mountplatform 300 with respect thereto about the longitudinal axis 308 (asindicated by an arrow C in FIG. 21). The outer wall 422 of the indexcollar 420 includes a plurality of hemispherical recesses 450 that canreceive one or more ball plungers 350 on the endoscope mount platform300 (indicated in dashed line.) This arrangement permits the endoscopemount platform 300, along with the endoscope 500, to be fixed in aplurality of discrete angular positions. Further details of the supportarm and indexing collar are described in U.S. Pat. No. 6,361,488, issuedMar. 26, 2002, U.S. Pat. No. 6,530,880 issued Mar. 11, 2003, andapplication Ser. No. 09/940,402 filed Aug. 27, 2001.

FIG. 24 shows one embodiment of the endoscope 500, which has anelongated configuration that extends into the expandable conduit 20 inorder to view the surgical site. In particular, the endoscope 500 has anelongated rod portion 502 and a body portion 504 which is substantiallyperpendicular thereto. In the illustrated embodiment, the rod portion502 of endoscope 500 has a diameter of about 4 mm and a length of about106 mm. Body portion 504 may define a tubular portion 506 which isconfigured to be slidably received in the bore 326 of endoscope mount320 as indicated by an arrow D. The slidable mounting of the endoscope500 on the endoscope mount platform 300 permits the endoscope 500 toadjust to configurations that incorporate different conduit diameters.Additional mobility of the endoscope 500 in viewing the surgical sitemay be provided by rotating the endoscope mount platform 300 about thecentral axis 308 (as indicated by arrow C in FIG. 21).

The rod portion 502 supports an optical portion (not shown) at a distalend 508 thereof, which may define a field of view of about 105 degreesand a direction of view 511 of about 25-30 degrees. An eyepiece 512 ispositioned at an end portion of the body portion 504. A camera (notshown) preferably is attached to the endoscope 500 adjacent the eyepiece512 with a standard coupler unit. A light post 510 supplies illuminationto the surgical site at the distal end portion 508. A preferred camerafor use in the system and procedures described herein is a three chipunit that provides greater resolution to the viewed image than a singlechip device.

A subsequent stage in the procedure involves placing the support arm 400and the endoscope mount platform 300 on the proximal portion, e.g., theproximal end 25, of the expandable conduit 20 (FIGS. 1 and 22), andmounting of the endoscope 500 on the endoscope mount platform 300. Anext step is insertion of one or more surgical instruments into theexpandable conduit 20 to perform the surgical procedure on the bodystructures at least partially within the operative space defined by theexpanded portion of the expandable conduit. FIG. 25 shows that in onemethod, the skirt portion 24 of expandable conduit 20 at least partiallydefines a surgical site or operative space 90 in which the surgicalprocedures described herein may be performed. Depending upon the overlapof the skirt portion, the skirt portion may define a surface which iscontinuous about the circumference or which is discontinuous having oneor more gaps where the material of the skirt portion does not overlap.

One procedure performable through the expandable conduit 20, describedin greater detail below, is a two-level spinal fixation. Surgicalinstruments inserted into the expandable conduit may be used fordebridement and decortication. In particular, the soft tissue, such asfat and muscle, covering the vertebrae may be removed in order to allowthe physician to visually identify the various “landmarks,” or vertebralstructures, which enable the physician to locate the location forattaching a fastener, such a fastener 600, discussed below, or otherprocedures, as will be described herein. Allowing visual identificationof the vertebral structures enables the physician to perform theprocedure while viewing the surgical area through the endoscope,microscope, loupes, etc., or in a conventional, open manner.

Tissue debridement and decortication of bone are completed using one ormore debrider blades, bipolar sheath, high speed burr, and additionalconventional manual instruments. The debrider blades are used to excise,remove and aspirate the soft tissue. The bipolar sheath is used toachieve hemostasis through spot and bulk tissue coagulation. Thedebrider blades and bipolar sheath are described in greater detail inU.S. Pat. No. 6,193,715, assigned to Medical Scientific, Inc., which isincorporated by reference in its entirety herein. The high speed burrand conventional manual instruments are also used to continue to exposethe structure of the vertebrae.

A subsequent stage is the attachment of fasteners to the vertebrae V.Prior to attachment of the fasteners, the location of the fastenerattachment is confirmed. In the exemplary embodiment, the pedicle entrypoint of the L5 vertebrae is located using visual landmarks as well aslateral and A/P fluoroscopy, as is known in the art. With continuedreference to FIG. 25, the entry point 92 is prepared with an awl 550.The pedicle hole 92 is completed using instruments known in the art suchas a straight bone probe, a tap, and a sounder. The sounder, as is knownin the art, determines whether the hole that is made is surrounded bybone on all sides, and that there has been no perforation of the pediclewall.

After hole in the pedicle is provided at the entry point 92 (or at anypoint during the procedure), an optional step is to adjust the locationof the distal portion of the expandable conduit 20. This may beperformed by inserting the expander apparatus 200 into the expandableconduit 20, expanding the distal portions 210, and contacting the innerwall of the skirt portion 24 to move the skirt portion 24 to the desiredlocation. This step may be performed while the endoscope 500 ispositioned within the expandable conduit 20, and without substantiallydisturbing the location of the proximal portion of the expandableconduit 20 to which the endoscope mount platform 300 may be attached.

FIGS. 26-27 illustrate a fastener 600 that is particularly applicable ina procedures involving fixation. The fastener 600 is described ingreater detail in U.S. patent application Ser. No. 10/075,668, filedFeb. 13, 2002 and application Ser. No. 10/087,489, filed Mar. 1, 2002,which are incorporated by reference in their entirety herein. Fastener600 includes a screw portion 602, a housing 604, a spacer member 606, abiasing member 608, and a clamping member, such as a cap screw 610. Thescrew portion 602 has a distal threaded portion 612 and a proximal,substantially spherical joint portion 614. The threaded portion 612 isinserted into the hole 92 in the vertebrae, as will be described below.The substantially spherical joint portion 614 is received in asubstantially annular, part spherical recess 616 in the housing 604 in aball and socket joint relationship (see also FIG. 29).

As illustrated in FIG. 27, the fastener 600 is assembled by insertingthe screw portion 602 into a bore in a passage 618 in the housing 604,until the joint portion 614 engages the annular recess 616. The screwportion 602 is retained in the housing 604 by the spacer member 606 andbiasing member 608. The biasing member 608 provides a biasing force todrive the spacer member 606 in frictional engagement with the jointportion 614 of the screw member 602 and the annular recess 616 of thehousing 604. The biasing provided by the biasing member 602 frictionallymaintains the relative positions of the housing 604 with respect to thescrew portion 602. The biasing member 608 is selected such that biasingforce prevents unrestricted movement of the housing 604 relative to thescrew portion 602. However, the biasing force is insufficient to resistthe application of force by a physician to move the housing 604 relativeto the screw portion 602. In other words, this biasing force is strongenough maintain the housing 604 stationary relative to the screw portion602, but this force may be overcome by the physician to reorient thehousing 604 with respect to the screw member 602, as will be describedbelow.

In the illustrated embodiment, the biasing member 608 is a resilientring having a gap 620, which permits the biasing member 608 to radiallycontract and expand. FIG. 27( a) illustrates that the biasing member 608may have an arched shape, when viewed end-on. The arched shape of thespring member 608 provides the biasing force, as will be describedbelow. The spacer member 606 and the biasing member 608 are insertedinto the housing 604 by radially compressing the biasing member into anannular groove 622 in the spacer member 606. The spacer member 606 andthe biasing member 608 are slid into the passage 618 until the distalsurface of the spacer member 606 engages the joint portion 614 of thescrew portion 602, and the biasing member 608 expands radially into theannular groove 622 in the housing 604. The annular groove 622 in thehousing 604 has a dimension 623 which is smaller than the uncompressedheight of the arched shape of the biasing member 608. When the biasingmember 608 is inserted in the annular groove 620, the biasing member 608is flattened against its normal bias, thereby exerting the biasing forceto the spacer member 606. It is understood that similar biasing members,such as coiled springs, belleville washers, or the like may be used tosupply the biasing force described herein.

The spacer member 606 is provided with a longitudinal bore 626, whichprovides access to a hexagonal recess 628 in the proximal end of thejoint portion 614 of the screw member 602. The proximal portion of thehousing 604 includes a pair of upright members 630 and 631 that areseparated by substantially “U”-shaped grooves 632. A recess forreceiving elongated member 650 is defined by the pair of grooves 632between upright member 630 and 631. Elongated member 650 to be placeddistally into the housing 604 in an orientation substantially transverseto the longitudinal axis of the housing 604, as will be described below.The inner walls of the upright members 630 and 631 are provided withthreads 634 for attachment of the cap screw 610 by threads 613 therein.

The fastener 600 is inserted into the expandable conduit 20 and guidedto the prepared hole 92 in the vertebrae as a further stage of theprocedure. The fastener 600 must be simultaneously supported and rotatedin order to be secured in hole 92. In the illustrated embodiment thefastener 600 is supported and attached to the bone by an endoscopicscrewdriver apparatus 660, illustrated in FIGS. 28-29. The screwdriver660 includes a proximal handle portion 662 (illustrated in dashed line),an elongated body portion 664, and a distal tool portion 666.

The distal tool portion 666, as illustrated in greater detail in FIG. 29includes a substantially hexagonal outer periphery which is received inthe substantially hexagonal recess 628 in the joint portion 614 of thescrew member 602. A spring member at the distal tool portion 666releasably engages the hexagonal recess 628 of the screw member 602 tosupport the fastener 600 during insertion and tightening. In theillustrated embodiment, a spring member 672 is configured to engage theside wall of the recess 628. More particularly, a channel/groove isprovided in the tip portion 666 for receiving the spring member 672. Thechannel/groove includes a medial longitudinal notch portion 676, aproximal, angled channel portion 678, and a distal substantiallytransverse channel portion 680. The spring member 672 is preferablymanufactured from stainless steel and has a medial portion 682 that ispartially received in the longitudinal notch portion 676, an angledproximal portion 684 which is fixedly received in the angled channelportion 678, and a transverse distal portion 686 which is slidablyreceived in the transverse channel 680. The medial portion 682 of thespring member 672 is partially exposed from the distal tip portion 666and normally biased in a transverse outward direction with respect tothe longitudinal axis (indicated by arrow E), in order to supply bearingforce against the wall of the recess 628. Alternatively the distal tipportion of the screw driver may be magnetized in order to hold the screwportion 602. Similarly, the distal tip portion may include a ballbearing or similar member which is normally biased in a radially outwarddirection to engage the interior wall of the recess 628 to secure thefastener 600 to the screwdriver distal tip 666.

The insertion of the fastener 600 into the prepared hole 92 may beachieved by insertion of screwdriver 660 into conduit 20 (indicated byarrow G). This procedure may be visualized by the use of the endoscope500 in conjunction with fluoroscopy. The screw portion 602 is threadedinto the prepared hole 92 by the endoscopic screwdriver 660 (indicatedby arrow H). The endoscopic screwdriver 660 is subsequently separatedfrom the fastener 600, by applying a force in the proximal direction,and thereby releasing the distal tip portion 666 from the hexagonalrecess 628 (e.g., causing the transverse distal portion 686 of thespring member 672 to slide within the transverse recess 680 against thebias, indicated by arrow F), and removing the screwdriver 660 from theexpandable conduit 20. An alternative method may use a guidewire, whichis fixed in the hole 92, and a cannulated screw which has an internallumen (as is known in the art) and is guided over the guidewire into thehole 92. The screwdriver would be cannulated as well to fit over theguidewire.

For a two-level fixation, it may be necessary to prepare several holesand attach several fasteners 600. The expandable conduit 20 can be sizedin order to provide simultaneous access to all vertebrae in which thesurgical procedure is being performed. In some cases, however,additional enlargement or repositioning of the distal portion of theexpandable conduit may be required in order to have sufficient access tothe outer vertebrae, e.g., the L4 and S1 vertebrae. In the illustratedembodiment, the expander apparatus 200 may be repeatedly inserted intothe expandable conduit 20 and expanded in order to further open orposition the skirt portion 24. In one procedure, additional fastenersare inserted in the L4 and S1 vertebrae in a similar fashion as thefastener 600 inserted in to the L5 vertebra as described above. (Whendiscussed individually or collectively, a fastener and/or its individualcomponents will be referred to by the reference number, e.g., fastener600, housing 604, and all fasteners 600. However, when several fastenersand/or their components are discussed in relation to one another, analphabetic subscript will be used, e.g., fastener 600 a is moved towardsfastener 600 b.)

In a further stage of the procedure, the housing portions 604 of thefasteners 600 are substantially aligned such that their upright portions630 and 631 face upward, and the notches 632 are substantially alignedto receive the elongated member 650 therein. The frictional mounting ofthe housing 604 to the screw member 602, described above, allows thehousing 604 to be temporarily positioned until a subsequent tighteningstep, described below. Positioning of the housing portions 604 may beperformed by the use of an elongated surgical instrument capable ofcontacting and moving the housing portion to the desired orientation.One such instrument for positioning the housings 604 is a grasperapparatus 700, illustrated in FIG. 30. The grasper apparatus 700includes a proximal handle portion 702, an elongated body portion 704,and distal nose portion 706. The distal nose portion 706 includes a pairof grasping jaws 708 a and 708 b, which are pivotable about pin 710 byactuation of the proximal handle portion 702. The grasping jaws 708 aand 708 b are illustrated in the closed position in FIG. 30. As is knownin the art, pivoting the movable handle 714 towards stationary handle714 causes longitudinal movement of actuator 716, which in turn pivotsthe jaw 708 b towards an open position (illustrated in dashed line). Thebiasing members 718 and 720 are provided to return the handles 712 and714 to the open position and bias the jaws 708 a and 708 b to the closedposition.

A subsequent stage in the process is the insertion of the elongatedmember 650 into the expandable conduit. The elongated member 650 ismanufactured from a biocompatible material and must be sufficientlystrong to maintain the positioning of the vertebrae, or other bodystructures. In the exemplary embodiment, the elongated members 650 aremanufactured from Titanium 6/4 or titanium alloy. Alternatively, theelongated member 650 may be manufactured from stainless steel or othersuitable material. The radii and length of the elongated members 650 areselected by the physician to provide the best fit for the positioning ofthe screw heads. Such selection may be performed by placing theelongated member 650 on the skin of the patient overlying the locationof the fasteners and viewed fluoroscopically. For example, a 70 mmpreformed rod having a 3.5″ bend radius may be selected for the spinalfixation.

The elongated member 650 is subsequently fixed to each of the fasteners600, and more particularly, to the housings 604 of each fastener 600.The grasper apparatus 700, described above, is also particularly usefulfor inserting the elongated member 650 into the expandable conduit 20and positioning it with respect to each housing 604. As illustrated inFIG. 30, the jaws 708 a and 708 b of the grasper apparatus 700 each hasa curved contact portion 722 a and 722 b for contacting and holding theouter surface of the elongated member 650.

As illustrated in FIG. 31, the grasper apparatus 700 may be used toinsert the elongated member 650 into the operative space 90 defined atleast partially by the skirt portion 24 of the expandable conduit 20.The cut-out portions 56 and 58 provided in the skirt portion 24 assistin the process of installing the elongated member 650 with respect tothe housings 604. The cut-out portions 56 and 58 allow an end portion652 of the elongated member 650 to extend beyond the operative spacewithout raising or repositioning the skirt portion 24. The elongatedmember 650 is positioned within the recesses in each housing 604 definedby grooves 632 disposed between upright members 630 and 631. Theelongated member 650 is positioned in an orientation substantiallytransverse to the longitudinal axis of each housing 604.

Further positioning of the elongated member 650 may be performed byguide apparatus 800, illustrated in FIG. 32. Guide apparatus 800 isuseful in cooperation with an endoscopic screwdriver, such as endoscopicscrewdriver 660 (illustrated in FIG. 28), in order to position theelongated member 650, and to introduce and tighten the cap screw 610,described above and illustrated in FIG. 27. Tightening of the cap screw610 with respect to the housing 604 fixes the orientation of the housing604 with respect to the screw portion 602 and fixes the position of theelongated member 650 with respect to the housing 604.

In the illustrated embodiment, the guide apparatus 800 has a proximalhandle portion 802, an elongated body portion 804, and a distal toolportion 806. The elongated body portion 804 defines a central bore 808(illustrated in dashed line) along its longitudinal axis 810. Thecentral bore 808 is sized and configured to receive the endoscopicscrewdriver 660 and cap screw 610 therethrough. In the exemplaryembodiment, the diameter of the central bore 808 of the elongated bodyportion 804 is about 0.384-0.388 inches in diameter, and the externaldiameter of the endoscopic screwdriver 660 (FIG. 28) is about 0.25inches. The proximal handle portion 802 extends transverse to thelongitudinal axis 810, which allows the physician to adjust the guideapparatus 800 without interfering with the operation of the screwdriver660.

The distal portion 806 of the apparatus includes several semicircularcut out portions 814 which assist in positioning the elongated member650. As illustrated in FIG. 33, the cut out portions 814 are sized andconfigured to engage the surface of elongated member 650 and move theelongated member 650 from an initial location (illustrated in dashedline) to a desired location.

As illustrated in FIG. 34, the guide apparatus 800 is used incooperation with the endoscopic screwdriver 660 to attach the cap screw610. The distal end of the body portion 804 includes a pair of elongatedopenings 816, which permit the physician to endoscopically view the capscrew 610 retained at the distal tip 666 of the endoscopic screw driver660.

The guide apparatus 800 and the endoscopic screwdriver 660 may cooperateas follows. The guide apparatus 800 is configured to be positioned in asurrounding configuration with the screwdriver 600. In the illustratedembodiment, the body portion 804 is configured for coaxial placementabout the screwdriver 660 in order to distribute the contact force ofthe guide apparatus 800 on the elongated member 650. The distal portion806 of the guide apparatus 800 may bear down on the elongated member 650to seat the elongated member 650 in the notches 632 in the housing 604.The “distributed” force of the guide apparatus 800 may contact theelongated member 650 on at least one or more locations. In addition, thediameter of central bore 808 is selected to be marginally larger thanthe exterior diameter of cap screw 610, such that the cap screw 610 mayfreely slide down the central bore 808, while maintaining theorientation shown in FIG. 34. This configuration allows the physician tohave effective control of the placement of the cap screw 610 into thehousing 604. The cap screw 610 is releasably attached to the endoscopicscrewdriver 660 by means of spring member 672 engaged to the interiorwall of hexagonal recess 611 as it is inserted within the bore 808 ofthe body portion 804 of guide apparatus 800. The cap screw 610 isattached to the housing 604 by engaging the threads 615 of the cap screw610 with the threads 634 of the housing.

As illustrated in FIG. 35, tightening of the cap screw 610 fixes theassembly of the housing 604 with respect to the elongated member 650. Inparticular, the distal surface of the cap screw 610 provides a distalforce against the elongated member 650, which in turn drives the spacermember 606 against the joint portion 614 of the screw portion 602, whichis consequently fixed with respect to the housing 604.

If locations of the vertebrae are considered acceptable by thephysician, then the fixation procedure is substantially complete oncethe cap screws 610 have been attached to the respective housings 604,and tightened to provide a fixed structure as between the elongatedmember 650 and the various fasteners 600. However, if compression ordistraction of the vertebrae with respect to one another is requiredadditional apparatus would be used to shift the vertebrae prior to finaltightening all of the cap screws 610.

In the illustrated embodiment, this step is performed with a surgicalinstrument, such as compressor-distractor instrument 900, illustrated inFIG. 36, which is useful to relatively position bone structures in thecephcaudal direction and to fix their position with respect to oneanother. Thus, the compressor-distractor instrument 900 has thecapability to engage two fasteners 600 and to space them apart whilesimultaneously tightening one of the fasteners to fix the spacingbetween the two vertebrae, or other bone structures. Moreover, thecompressor-distractor instrument 900 may also be used to move twofasteners 600, and the vertebrae attached thereto into closerapproximation and fix the spacing therebetween.

The distal tool portion 902 of the compressor-distractor instrument 900is illustrated in FIG. 36. (Further details of the compressor-distractorapparatus is described in co-pending U.S. application Ser. No.10/178,875, filed Jun. 24, 2002, entitled “Surgical Instrument forMoving Vertebrae,” which is incorporated by reference in its entiretyherein.) The distal tool portion 902 includes a driver portion 904 and aspacing member 906. The driver portion 904 has a distal end portion 908with a plurality of wrenching flats configured to engage the recess 611in the proximal face of the cap screw 610, and to apply torque to thecap screw. The driver portion 904 is rotatable about the longitudinalaxis (indicated by arrow M) to rotate the cap screw 610 relative to thefastener 600. Accordingly, the driver portion 904 can be rotated toloosen the cap screw 610 on the fastener 600 and permit movement of theelongated member 650 connected with the vertebra relative to thefastener 600 connected with the vertebra. The cap screw 610 can also berotated in order to tighten the cap screw 610 and clamp the elongatedmember 650 to the fastener 600.

The distal tool portion 902 may also include a spacing member, such asspacing member 906, which engages an adjacent fastener 600 b whiledriver member 904 is engaged with the housing 604 a to move the fastener600 b with respect to the fastener 600 a. In the exemplary embodiment,spacing member 906 is a jaw portion which is pivotably mounted to movebetween a first position adjacent the driver portion and a secondposition spaced from the driver portion, as shown in FIG. 36. The distaltip 910 of the spacing member 906 is movable relative to the driverportion 904 in a direction extending transverse to the longitudinalaxis.

As illustrated in FIG. 36, the spacer member 906 can be opened withrespect to the driver portion 904 to space the vertebrae further apart(as indicated by arrow N). The distal portion 910 of the spacer member906 engages the housing 604 b of fastener 600 b and moves fastener 600 bfurther apart from fastener 600 a to distract the vertebrae. Where thevertebrae are to be moved closer together, e.g. compressed, the spacermember 906 is closed with respect to the driver portion 904 (arrow P),as illustrated in FIG. 37. The distal portion 610 of spacer member 606engages housing 604 b of fastener 600 b and moves fastener 600 b towardsfastener 600 a. When the spacing of the vertebrae is acceptable to thephysician, the cap screw 610 a is tightened by the driver member 904,thereby fixing the relationship of the housing 604 a with respect toelongated member 650, and thereby fixing the position of the vertebrae,or other bone structures, with respect to one another.

Once the elongated member 650 is fixed with respect to the fasteners600, the procedure is substantially complete. The surgicalinstrumentation, such as the endoscope 500 is withdrawn from thesurgical site. The expandable conduit 20 is also withdrawn from thesite. The muscle and fascia can be allowed to close as the expandableconduit 20 is withdrawn through the dilated tissues in the reducedprofile configuration. The fascia and skin incisions are closed in thetypical manner, with sutures, etc. The procedure described above may berepeated for the other lateral side of the same vertebrae, if indicated.

II. Motion Preserving Stabilization Systems

Another type of procedure that can be performed by way of the systemsand apparatuses described hereinabove provides stabilization of skeletalportions, e.g. adjacent vertebrae in the spine, as would be the case inmore conventional fixation procedures, but advantageously preserves adegree of normal motion. A variety of system and methods that may beused to provide motion preserving stabilization, such as dynamicstabilization, are described below. The access devices and systemsdescribed above enable these systems and methods to be practicedminimally invasively.

A. Stabilization Devices Allowing Axial Motion

A first type of motion preserving stabilization device is shown in FIGS.38-40. In the illustrated embodiment, the motion preservingstabilization device 1000 is attached on the posterior side of thespine. However, the device 1000 may be modified for use on the anterioror lateral sides of the spine, or at locations between the anterior andlateral sides, or at locations between the lateral and posterior sides,e.g., at a posterolateral location. In one embodiment, the components ofthis stabilization device 1000 may be fabricated from a biocompatiblemetal, preferably titanium or a titanium alloy. The components may alsobe fabricated from other metals, or other suitable materials.

In one embodiment, the stabilization device 1000 comprises a plate 1004,a plurality of fasteners 1008, a plurality of fastener clamp portions1012 and 1016, fastener spacers 1020, and stop locks 1024, as shown inFIGS. 38-40. The stabilization device 1000 and its components arefurther described in the following paragraphs.

In one embodiment, the plate 1004 is the framework upon which the othercomponents are attached. In one embodiment, the plate 1004 is anelongate member having a caudal end and a cephalad end, and defining alongitudinal axis extending from the caudal end to the cephalad end. Theplate 1004 may have a slot parallel to its longitudinal axis to receiveand contain the fasteners 1008. The slot advantageously allows thefasteners 1008 to be infinitely positioned axially to place it into thedesired position relative to the vertebra. The plate optionally may beformed from a single piece of metal. Another approach would be toprovide preformed holes, which would limit the location of the fasteners1008 with respect to the plate 1004. The plate 1004 may be curved orotherwise shaped or configured to allow for stabilizing a spine orpositioning individual vertebrae as required. Although not shown, theplate 1004 may have one or more open ends. The open ends can enabledifferent fastener elements to be more easily inserted, and may then beclosed and stiffened with one or more stop locks 1024. In anotherembodiment, the slot need not extend the entire length of the plate1004, but can provide a more limited range of potential axial positions.In another embodiment, the plate 1004 may have a more rod-like shapewith a hollowed out portion adapted to engage a portion of the fasteners1008. In another embodiment, the plate 1004 may incorporate a hinge bywhich it is attached to at least one fastener 1008, such that the atleast one fastener 1008 can move with respect to at least one otherfastener 1008.

In FIG. 39, a partial cross-sectional view of one embodiment of thefastener 1008 is shown. The fastener 1008 may comprise a bone screw,such as a conventional pedicle screw similar to the fastener 600described above. The fastener has tapered screw threads 1028 at a boneend 1032, a head which will accept a tool near a midsection 1036, and amachine screw threaded stud 1040 at a clamp end. In other embodiments,in place of a bone screw, other fastener means, such as straight pins ortapered pins, bone hooks, or others, may be used to provide attachmentwith the bone. In one embodiment, the fastener may also have ascrewdriver slot to adjust the screw height as shown in FIG. 40.

In one embodiment, the fastener 1008 is attached to the plate 1004 viathe fastener clamp portions 1012 and 1016, shown in FIG. 40 and moreclearly in the detailed view shown in FIG. 40. In one embodiment, a nut1044 clamps the upper fastener clamp portion 1012, through the plate1004, to the lower fastener clamp portion 1016, and against a collar1048 on the fastener 1008 to give metal-to-metal clamping. Because ofthe metal-to-metal clamping, the fastener 1008 does not requireanti-rotational locks such as auxiliary screw clamps, cams, wedges orlocking caps. The metal-to-metal clamping of the fastener 1008 to theplate 1004 provides a fully rigid bone stabilizer system. In otherembodiments, other means of attaching the plate 1004 to the fasteners1008 may be used. The fastener clamp portions 1012 and 1016 may bemachined to angular shapes to allow the fastener 1008 to be attached tothe plate 1004 at different angles.

In one application, spacers 1020 are selectively installed between thefastener clamp portions 1012 and 1016 to allow axial motion of thefasteners 1008 along the slot with respect to the plate 1004. Thisspacer 1020 installation may preserve motion between the fasteners 1008and the plate 1004. A spacer 1020 is a piece of material with a widthgreater than the width of the plate 1004 placed between the fastenerclamp portions 1012 and 1016, such that the fastener clamp portions 1012and 1016 fixedly contact the spacer 1020 and not the plate 1004. In oneembodiment, because of the metal-to-metal clamping through the spacer1020, auxiliary screw clamps such as a cam, a wedge or a locking cap maynot be needed. To reduce the number of small parts, the lower fastenerclamp portion 1016 and the spacer 1020 may optionally be fabricated asone integral part. If desired, in a rigid installation without a spacer1020, the nut 1044 may force the fastener clamp portions 1012 and 1016directly against the plate 1004.

In one embodiment, the stop locks 1024 may be clamped to the plate 1004to maintain plate rigidity, and they may serve as travel limit stops topreserve or to favor motion in one direction and to limit or eliminateit in the opposite direction. This action is sometimes referred toherein as unidirectional, dynamized action of the fasteners 1008 withrespect to the plate 1004. In one embodiment, the motion of thefasteners 1008 in a cephcaudal direction is limited. In one embodiment,the stop lock 1024 includes an upper portion, a lower portion, and ascrew, which assembly can be attached to the plate 1004 in a similarmanner to the fastener clamp portions 1012 and 1016 described above. Thestop locks 1024 may be preloaded before tightening the stop lock screw.The stop locks 1024 may also utilize springs or other force generatingmeans to maintain compression on the vertebra/graft interface.

FIG. 38 shows that two stabilization devices 1000 can be used inconjunction on either side of the spinous processes, extending acrossthree vertebrae. The stabilization device 1000 may alternatively beapplied with one or more plates, and they may extend across two or morevertebrae.

In one embodiment, the unidirectional, dynamized action between thefasteners 1008 and plate 1004 preserves subsidence of the vertebrae,motion of an upper vertebra in a caudal direction. Among otheradvantages, this allows for graft resorption and settling. It alsoprovides improved fusion conditions and prevents graft distraction. Thestabilization device 1000 can also provide stress shielding to thestabilized vertebrae along other directions, including: rotation causingaxial shear; lateral bending causing contralateral distraction; flexioncausing posterior distraction; extension causing anterior distraction;horizontal force causing translation shear; and extension causingdistraction.

Further details of structures that provide support and stability whilepreserving motion may be found in U.S. patent application Ser. No.09/846,956 filed on May 1, 2001, published as U.S. Patent ApplicationNo. 2001/0037111 on Nov. 1, 2001, which is hereby incorporated byreference in its entirety.

FIG. 41 shows another, similar embodiment of a motion preservingstabilization device 1100, which includes rods 1104, 1108 interconnectedby a pair of plates 1112, 1116 each secured to a respective vertebra bymultiple fasteners. In one embodiment, although the FIGURE shows ananterior insertion, the stabilization device 1100 is configured to besecured to the posterior side of the spine. The device 1100 may also bemodified for use on the anterior or lateral sides of the spine, or at alocation between the anterior and lateral sides, or at a locationbetween the lateral and posterior sides, e.g., posterolateral.

In one embodiment, the stabilization device 1100 comprises a pair ofsurgically implantable rods 1104 and 1108. The stabilization device 1100may also include first and second plates 1112 and 1116, which engage therods 1104 and 1108; three fasteners 1120, 1124, and 1128 for connectingthe first plate 1112 with the first vertebra V1; and three fasteners1132, 1136, and 1140 for connecting the second plate 1116 with thesecond vertebra V2.

The first rod 1104 is made of a suitable biocompatible material, such astitanium or stainless steel. In one embodiment, the first rod 1104 hasan elongate cylindrical configuration and has a circular cross sectiontaken in a plane extending perpendicular to the longitudinal centralaxis of the first rod. The first rod 1104 may also have a smooth outersurface. A first end portion of the first rod 1104 may comprise a cap1144. The first rod 1104 may also have a second end portion 1148opposite from the cap 1144. In one embodiment, the rod 1104 has auniform diameter of about three (3) millimeters throughout its extentexcept at the cap 1144.

The second rod 1108 may be substantially identical to the first rod1104. In one embodiment, the second rod 1108 has a first end portioncomprising a cap 1152. The second rod 14 may also have a second endportion 1156 opposite from the cap 1152. In one embodiment, the rods1104 and 1108 are bendable to a desired configuration to conform to adesired curvature of the spinal column. In a preferred embodiment, therods 1104 and 1108 together have sufficient strength and rigidity tomaintain the vertebrae V1 and V2 in a desired spatial relationship.

In one embodiment, the rods 1104 and 1108 have a length sufficient toenable them to span at least the two vertebrae V1 and V2. The length ofthe rods 1104 and 1108 will depend upon the condition to be correctedand the number of vertebrae to be held in a desired spatial relationshiprelative to each other by the stabilization device 1100. If more thantwo vertebrae are to be held in a desired spatial relationship relativeto each other by the stabilization device 1100, the rods 1104 and 1108could be longer, and more than two plates, such as the plates 1112 and1116, may be used.

The first plate 1112 may be made of any suitable biocompatible material,such as titanium or stainless steel. In one embodiment, the first plate1112 includes a main body portion. The main body portion of the firstplate 1112 may have a planar outer side surface for facing away from thefirst vertebra V1. The first plate 1112 may have an arcuate inner sidesurface for facing toward the first vertebra V1. The inner side surfaceof the first plate 1112 may engage the surface of the first vertebra V1when the first plate is connected with the first vertebra as describedbelow.

The main body portion of the first plate 1112 may also have a centralportion which extends laterally between a first side portion 1160 and asecond side portion 1164 of the first plate 1112. Because the inner sidesurface of the first plate 1112 has an arcuate configuration, thecentral portion of the first plate 1112 may be relatively thin ascompared to the first side portion 1160 and to the second side portion1164.

In one embodiment, the main body portion of the first plate 1112 alsohas first and second end portions 1168 and 1172. The first end portion1168 of the first plate 1112 may include a planar first end surface ofthe first plate 1112. The second end portion 1172 may include a planarsecond end surface of the first plate 1112. The second end surface mayextend parallel to the first end surface.

In one embodiment, a first rod passage is formed in the first sideportion 1160 of the first plate 1112. The first rod passage is anopening that extends between the first and second end surfaces of thefirst plate 1112, in a direction parallel to the planar outer sidesurface of the first plate 1112. The first rod passage may be defined bya cylindrical surface and tapered pilot surfaces and at opposite ends ofthe cylindrical surface. The diameter of the cylindrical surface isoptionally slightly greater than the diameter of the first rod 1104, sothat the first rod 1104 and the first plate 1112 can be relativelymovable.

In one embodiment, the second side portion 1164 of the first plate 1112is a mirror image of the first side portion 1160. A second rod passageis formed in the second side portion 1164 of the first plate 1112. Thesecond rod passage is an opening that extends between the first andsecond end surfaces of the first plate 1112, in a direction parallel tothe planar outer side surface of the first plate 1112. The second rodpassage extends parallel to the first rod passage. In one embodiment,the second rod passage is defined by a cylindrical surface and taperedpilot surfaces at opposite ends of the cylindrical surface. The diameterof the second rod passage is preferably the same as the diameter of thefirst rod passage. The diameter of the cylindrical surface is optionallyslightly greater than the diameter of the second rod 1108, so that thesecond rod 1108 and the first plate 1112 can be relatively movable.

In one embodiment, a circular first fastener opening extends through thecentral portion of the first plate 1112. The first fastener opening hasan axis that extends perpendicular to the plane of the outer sidesurface of the first plate 1112. The first fastener opening may bepartially defined by a larger diameter cylindrical surface, whichextends from the outer side surface of the first plate 1112 in adirection into the material of the central portion of the first plate1112. The cylindrical surface is centered on the axis of the firstfastener opening. The first fastener opening may also be partiallydefined by a smaller diameter cylindrical surface, which extends fromthe inner side surface of the first plate 1112 in a direction into thematerial of the central portion of the first plate to a location spacedradially inward from the larger diameter cylindrical surface. Thissmaller diameter cylindrical surface may also be centered on the axis ofthe first fastener opening 90.

In one embodiment, an annular shoulder surface extends radially(relative to the axis of the first fastener opening 90) between thelarger and smaller diameter cylindrical surfaces. The shoulder surfaceand the larger diameter cylindrical surface define a recess in the outerside surface of the first plate 1112.

The main body portion of the first plate 1112 may also include acircular second fastener opening fanned at a location adjacent to, butspaced apart from, the first rod passage in the first side portion 1160of the first plate 1112. The second fastener opening may extend throughboth the second end surface of the first plate 1112 and the outer sidesurface of the first plate 1112. In one embodiment, the second fasteneropening is partially defined by a larger diameter cylindrical surface, asmaller diameter cylindrical surface and an annular shoulder surface, ina configuration similar to that of the first fastener opening.

The main body portion of the first plate 1112 may also include acircular third fastener opening formed at a location adjacent to, butspaced apart from, the second rod passage in the second side portion1164 of the first plate 1112. The third fastener opening may extendthrough both the second end surface of the first plate 1112 and theouter side surface of the first plate 1112. In one embodiment, the thirdfastener opening is partially defined by a larger diameter cylindricalsurface, a smaller diameter cylindrical surface and an annular shouldersurface, in a configuration similar to that of the first fasteneropening.

The second plate 1116 may be generally similar in configuration to thefirst plate 1112, with rod passages disposed on both sides. The secondplate 1116 may be configured, however, so that the head ends of thefasteners 1136, 1140 received in certain fastener openings in the secondplate 1116 are engageable with the rods 1104 and 1108 disposed in rodpassages in the second plate 1116. This engagement can block movement ofthe second plate 1116 relative to the rods 1104 and 1108, in a mannerdescribed below.

One or both of the fastener openings receiving the fasteners 1136 or1140 may be partially defined by a larger diameter cylindrical surfacewhich extends from the outer side surface of the second plate 1116 in adirection into the material of the first side portion of the secondplate. This larger diameter cylindrical surface is centered on an axisof the fastener opening. The larger diameter cylindrical surface mayalso intersect the cylindrical surface that defines a rod passage in thesecond plate 1116. Thus, the fastener opening overlaps a portion of arod passage.

In one embodiment, the fasteners 1120, 1124, 1128, 1132, 1136, and 1140,which connect the first plate 1112 with the first vertebra V1, and thesecond plate 1116 with the second vertebra V2, may be identical to eachother. These fasteners 1120, 1124, 1128, 1132, 1136, 1140 may comprisebone screws, such as conventional pedicle screws similar to the fastener600 described above. In other embodiments, in place of a bone screw,other fastener means, such as straight pins or tapered pins, bone hooks,or others, may be used to provide attachment with the bone.

When the second plate 1116 is connected with the second vertebra V2, thefasteners 1132, 1136 and 1140 secure the second plate and the secondvertebra. The outer fasteners 1136 and 1140 may also serve to interlockthe second plate 1116 with the rods 1104 and 1108, by moving intoengagement with the rods 1104 and 1108, respectively, when each fasteneris fully screwed into a respective vertebra. In one embodiment, theengagement between the fasteners 1136 and 1140 and the rods 1104 and1108 blocks movement of the fasteners 1136 and 1140 relative to therods. As a result, the fasteners 1136 and 1140 may also block movementof the second plate 1116 relative to the rods 1104 and 1108. Other meansof blocking the movement of the second plate 1115 relative to the rods1104 and 1108 are well known to those of skill in the art.

In one embodiment, the first plate 1112, in contrast, preserves motionrelative to the rods 1104 and 1108, because the second and thirdfastener openings are spaced apart from the first plate's rod passages.In a preferred embodiment, the first plate 1112 is thus movable relativeto the second plate 1116. In other embodiments, this motion preservingstabilization system 1100 may consist of two or more movable plates like1112, with no fixed plates like 1116.

Accordingly, the first vertebra V1 may be movable vertically downwardrelative to the second vertebra V2. This relative movement allows forthe maintaining of a load on bone graft placed between the vertebrae V1and V2. If the first plate 1112 were not movable vertically downwardrelative to the second plate 1116, then the distance between thevertebrae V1 and V2 would be fixed. If bone graft were placed betweenthe vertebrae V1 and V2 and the bone graft resorbed sufficiently, thebone graft could possibly shrink out of engagement with one or both ofthe vertebrae V1 and V2. Allowing relative movement of the plates 1112and 1116 can help to maintain a load on bone graft placed between thevertebrae V1 and V2 and maintains the vertebrae in contact with the bonegraft to facilitate bone growth.

The caps 1144 and 1152 on the rods 1104 and 1108, respectively, limitmovement of the first vertebra V1 in a direction away from the secondvertebra V2. This helps to maintain the vertebrae V1 and V2 in contactwith the bone graft.

The stabilization device 1100 can also provide stress shielding to thestabilized vertebrae along other directions, including: rotation causingaxial shear; lateral bending causing contralateral distraction; flexioncausing posterior distraction; extension causing anterior distraction;horizontal force causing translation shear; and extension causingdistraction.

Further details of structures that provide support and stability whilepreserving motion may be found in U.S. Pat. No. 6,036,693 filed on Nov.30, 1998, which is hereby incorporated by reference in its entirety.

B. Stabilization Device Having a Flexible Elongate Member

FIG. 42 shows another embodiment of a motion preserving stabilizationdevice 1200. While the FIGURE shows one stabilization device 1200,extending across five vertebrae. As discussed more fully below, multiplestabilization devices 1200 may be applied to a spine in parallel, andmay extend across more or fewer vertebrae. The stabilization device 1200includes an elongate member 1204 secured to a plurality of fasteners1208. In one embodiment, each fastener 1208 is engaged to a respectiveone of the vertebrae V1, V2, V3, V4, V5. A coupling member 1212 isengaged to each of the fasteners 1208 with the elongate member 1204positioned between each fastener 1208 and its respective coupling member1212.

It should be understood that the stabilization device 1200 may beutilized in all regions of the spine, including the cervical, thoracic,lumbar, lumbo-sacral and sacral regions of the spine. Additionally,although the stabilization device 1200 is shown in FIG. 42 as havingapplication in a posterior region of the spine, it may alternatively beapplied in other surgical approaches and combinations of surgicalapproaches to the spine such that one or more stabilization devices 1200are attached to the anterior, antero-lateral, lateral, and/orpostero-lateral portions of the spine.

In one embodiment, the stabilization device 1200 allows at least smalldegrees of spinal motion between the vertebrae to which it is attached,since the stabilization device 1200 includes an elongate member 1204that is at least partially flexible between adjacent fasteners 1208. Itshould be understood that the stabilization device 1200 can be used inconjunction with fusion or non-fusion treatment of the spine. In oneembodiment, the elongate member 1204 is a tether made from one orpolymers, such as, for example, polyester or polyethylene; one or moresuperelastic metals or alloys, such as, for example, nitinol; or fromresorbable synthetic materials, such as, for example suture material orpolylactic acid. It is further contemplated that the elongate member1204 may have elasticity such that when tensioned it will tend to returntoward its pre-tensioned state. In other embodiments, the shape and sizeof the elongate member 1204 can be modified to adjust its elasticity andflexibility along different axes.

The fasteners 1208 and coupling members 1212 described herein may beemployed with the shown stabilization device 1200. In addition, it iscontemplated that the fasteners 1208 and coupling members 1212 describedherein may be employed in isolation or in devices that include two ormore coupling members 1212 and fasteners 1208. Examples of other devicesinclude: one or more elongate members 1204 extending laterally across avertebral body; one or more elongate members 1204 extending in theanterior-posterior directions across a vertebral body; one or moreelongate members 1204 wrapped around a vertebral body; and combinationsthereof. Further examples include application of the fasteners 1208 andcoupling members 1212 of the present disclosure with bony structures inregions other than the spinal column.

In one embodiment, a fastener 1208 may comprise a bone screw, such as aconventional pedicle screw similar to the fastener 600 described above.In other embodiments, in place of a bone screw, other fastener means,such as straight pins or tapered pins, bone hooks, or others, may beused to provide attachment with the bone. Similarly, a coupling member1212 may comprise a cap screw similar to the cap screw 610 describedabove. In another embodiment, the coupling member 1212 comprises athreadable portion to threadably engage the fastener 1208, and apenetrating element to penetrate the elongate member 1204. In otherembodiments, the coupling member 1212 may comprise another means ofengaging a fastener 1208 and the elongate member 1204.

The motion preserving elongate member 1204 of this stabilization device1200 enables adjacent vertebrae to move relative to each other dependingon the elongate member's 1204 flexibility, while partially reproducingthe restorative forces of a healthy spine. Moreover, the stabilizationdevice 1200 may be stiffer along the direction of the longitudinal axis,reducing the compressive forces imposed upon the intervertebral regions,and providing support for the spine's load-bearing functions.

Further details of structures that provide support and stability whilepreserving motion may be found in U.S. patent application Ser. No.10/013,053 filed on Oct. 30, 2001, published as U.S. Patent PublicationNo. 2003/0083657 on May 1, 2003, and U.S. patent application Ser. No.09/960,770 filed on Sep. 21, 2001, published as U.S. Patent PublicationNo. 2002/0013586 on Jan. 31, 2002, which are hereby incorporated byreference in their entirety.

C. Stabilization Device with a Jointed Link Rod

FIG. 43 illustrates a portion of another embodiment of a stabilizationdevice 1250. In one embodiment, the stabilization device 1250 isconfigured to be secured to the posterior side of the spine. However,the device 1250 may be modified for use on the anterior or lateral sidesof the spine, or at a location between the anterior and lateral sides,or at a location between the lateral and posterior sides, e.g.,posterolateral.

In the example shown in FIG. 43, a set of fasteners connected to atleast two vertebrae may be interconnected by a link rod 1254 comprisingat least two rigid segments 1254A and 1254B, which are interconnected bymeans of a damper element 1258 interposed between their facing freeends, so as to oppose elastic resistance between the segments 1254A and1254B with amplitude that may be controlled not only in axialcompression and traction a, but also in angular bending b.

A single link rod 1254 may include a plurality of dampers 1258 disposedbetween the vertebrae. Also, the link rod 1254 may advantageously be cutto a selected length and curved to a selected radius.

As can be seen more clearly in FIG. 43, the damper element 1258 may bemade up of two elastically deformable members 1258A disposed around thefree end of a pin 1254Ba extending from one of the segments 1254Bconstituting the rod 1254. The pin 1254Ba may be engaged inside ahousing 1262 a formed in a blind sleeve or cage 1262 made at the freeend 1254Aa of the other link segment 1254A. In one embodiment, thedamper element 1258 comprises a rigid piston 1266 formed on the pin1254Ba to constitute a joint 1266 making multidirectional relativepivoting possible between the cage 1262 and the pin 1254Ba, at leastabout axes contained in a plane perpendicular to the longitudinal axisx-x′ of the damper element 1258 when the pin 1254Ba and the cage 1262are in alignment.

In one embodiment, the resulting joint 1266 is of the ball-and-sockettype that also allows the cage 1262 to rotate relative to the pin 1254Baabout the axis x-x′. The joint 1266 may comprise a collar projectingradially from the pin 1254Ba and having an outside surface with arounded profile that is designed to come into contact with the insidesurface of the housing 1262 a in the cage 1262. In the embodiment shownin FIG. 43, the collar 1266 is an integral part of the pin 1254Ba,although in other examples, the collar 1266 may comprise a separate ringthat is fixed on the pin 1254Ba.

The collar 1266 is disposed relative to the pin 1254Ba in such a manneras to receive thrust on both of its lateral faces from two sets ofspring washers 1270 each in the form of a pair of facing frustoconicalcups of identical diameter stacked on the pin 1254Ba. The washers 1270and the joint 1266 occupy at least part of the circular section housing1262 a, whose end wall constitutes a compression abutment for one of theelastically deformable members 1258A. It should be observed that thespring washers 1270, which are also known as “Belleville” washers, canbe replaced by other spring-like elements, such as elastomer rings.

In one embodiment, the housing 1262 a of the cage 1262 is closed by afirst washer 1274 secured to the cage 1262 and having an inside faceagainst which there bears a second washer 1278 secured to the pin1254Ba. The deformable members 1258A may be placed freely on the pin1254Ba between the second washer 1278 and the end wall of the housing1262 a. For example, the first washer 1274, which constitutes an axialabutment, can be implemented in the form of a threaded ring screwed intotapping made inside the housing from its outer end, thereby making itpossible to adjust the extension position of the damper. It should beobserved that the second washer 1278, which is secured to the pin1254Ba, constitutes a bearing surface for an elastically deformablemember 1258A. This second washer 1278 can serve as an abutment for thedamper in axial traction. This second washer 1278 thus makes it possibleto exert compression force on the deformable member without damaging it.In addition, according to an advantageous characteristic, the secondwasher 1278 can be made of a material that is identical to thatconstituting the elastically deformable member, so as to make itpossible to control the friction which appears between the second washer1278 and the elastically deformable member 1258A.

The elastically deformable members 1258A are maintained with axialclearance that makes it possible, when they deform elastically, toaccommodate relative axial movements in compression and traction betweenthe pin 1254Ba and the cage 1262. For example, it is possible to obtainaxial compression or traction having a value of 0.8 mm. In addition, theelastically deformable members 1258A may be mounted to allowmultidirectional relative pivoting between the pin 1254Ba and the cage1262. The washers 1270 may therefore be mounted inside the housing 1262a with clearance relative to the inside wall of the housing.

In one embodiment, the damper element 1258 includes an angular abutmentfor limiting the multidirectional relative pivoting to a determinedvalue having an amplitude of about 4 degrees. Thus, as can be seen moreclearly in FIG. 43, the displacement b of the pin 1254Ba in the cage1262 relative to its normal, aligned position is 2 degrees. In theembodiment shown, the angular abutment is provided by the housing 1262 aagainst which the pin 1254Ba comes into abutment, which pin 1254Ba has apredetermined amount of radial clearance relative to the housing 1262 ato enable relative pivoting to take place through the predeterminedangle b. Thus, the pin 1254Ba presents radial clearance both between itscollar 1266 and the housing 1262 a, and between its free end and a blindrecess 1262 b extending the housing 1262 a. Relative pivoting betweenthe cage 1262 and the pin 1254Ba is thus limited by implementing twoangular abutments defined by the co-operation firstly between the collar1266 and the housing 1262 a, and secondly between the free end of thepin 1254Ba and the blind recess 1262 b. It should be observed that thetwo abutments constituted in this way are set up in opposition about theaxis x-x′. This allows limited bending to be obtained between the cageand the pin in all directions of angular displacement.

This motion preserving link rod 1254 of this stabilization device 1250enables adjacent vertebrae to move relative to each other depending onthe flexibility of the incorporated joint 1266, while partiallyreproducing the restorative forces of a healthy spine. Moreover, thestabilization device 1250 may be stiffer along the direction of thelongitudinal axis, reducing the compressive forces imposed upon theintervertebral regions, and providing support for the spine'sload-bearing functions.

Further details of structures that provide support and stability whilepreserving motion may be found in U.S. Pat. No. 6,241,730 filed on Nov.27, 1998, which is hereby incorporated by reference in its entirety.

D. Stabilization Device with a Spring Element

FIG. 44 illustrates another embodiment of a stabilization device 1300.In one embodiment, the stabilization device 1300 is configured to besecured to the posterior side of the spine. However, the device 1300 maybe modified for use on the anterior or lateral sides of the spine, or ata location between the anterior and lateral sides, or at a locationbetween the lateral and posterior sides, e.g., posterolateral.

In one embodiment, the body 1304 of the stabilization device 1300comprises a leaf spring 1308 in the form of a closed loop and in onepiece with fasteners 1312. The stabilization device 1300 is preferablymade of titanium or titanium alloy, although other biocompatiblematerials may be used. In one embodiment, the spring 1308 defines twoleaf spring parts 1308 a, 1308 b extending parallel to each other in thealignment direction 1316. The generatrix 1320 extends from front torear, and defines the moving straight line, whose path defines theplanar leaf spring 1308 of the stabilization device 1300.

The two parts 1308 a, 1308 b of the spring may be symmetrical to eachother with respect to a median plane passing through the axis 1316. Eachspring part forms a plurality of successive U-shapes alternatelyoriented in opposite directions in a plane perpendicular to thegeneratrix 1320. In one embodiment, each part 1308 a, 1308 b has threeof these U-shapes. The U-shapes nearest the fasteners 1312 have theirbase facing towards the outside of the stabilizing device 1300, and themiddle U-shape of each part has its base facing towards the inside ofthe stabilizing device 1300. Each part 1308 a, 1308 b therefore forms anundulation or zigzag. To be more precise, the general shape of thisembodiment is that of an inverted M.

In one embodiment, each fastener 1312 comprises two jaws 1328, which aresymmetrical to each other with respect to the median plane, generallyflat in shape and have a generatrix parallel to the generatrix 1320. Thetwo jaws 1328 face each other. Their facing faces have profiled teeth1332. Each jaw has a passage 1336 for inserting a tool for maneuveringthe jaw and whose axis is parallel to the generatrix 1320. The bases ofthe jaws 1328 extend at a distance from each other from one end of thespring 1308. The two jaws 1328 are mobile elastically relative to eachother. At rest they diverge from their base.

To fit the stabilizing device 1300, the jaws 1328 of each fastener 1312may be forced apart using tools inserted into the passages 1336. Thestabilizing device 1300 may then be placed as shown in FIG. 44 so thateach spinous process 1340 is between the respective jaws 1328. The jawsare then released so that they grip the processes and are anchored tothem by their teeth 1332.

The leaf spring parts 1308 a, 1308 b may extend laterally beyond thespinous processes 1340. They can be configured to impart a low stiffnessto them. A stabilizing device 1300 may optionally be fabricated by sparkerosion from a mass of metal; this fabrication process beingparticularly simple because of the profile of the device 1300. In oneembodiment, this stabilizing device 1300 has a relatively low stiffnessfor lateral flexing of the body, i.e. flexing about an axis parallel tothe generatrix 1320. It has a high stiffness for flexing of the bodyfrom front to rear, i.e. flexing about an axis perpendicular to thedirection 1316 and to the generatrix 1320. In other embodiments, theshape of the spring 1308 can easily be modified to increase or reduce atleast one of the stiffnesses referred to above, independently of thevolume available between the processes 1340.

Although the spring element 1308 resists deformation proportionally toan effective spring constant, its structure also preserves some amountof motion between adjacent vertebrae. In one embodiment, the spring 1308may be configured to allow some proportion of the axial forces to beimposed upon the intervertebral region, while providing restorativeforces. This motion preserving device thereby facilitates healing andshields the spine from some postoperative stress.

Further details of structures that provide support and stability whilepreserving motion may be found in U.S. Pat. No. 6,440,169 filed on Jan.27, 1999, which is hereby incorporated by reference in its entirety.

E. Stabilization Devices Comprising an Array of Elongated Elements

As discussed above, dynamic stabilization of the spine stabilizes adiseased or damaged motion segment while preserving at least a portionof the natural motion of the segment. Stabilization can augment thespine, restoring support of or natural stiffness to an unstable motionsegment. A motion segment includes, for example, a disk, or a disk and avertebra, or a pair of vertebrae and a disk sandwiched between the pair,or a larger portion of the spine.

FIG. 45 illustrates an embodiment of a dynamic stabilization apparatus1400. In one embodiment, the stabilization apparatus 1400 is configuredto be secured to the posterior side of the spine. The apparatus 1400 mayalso be modified for use on the anterior or lateral sides of the spine,or at a location between the anterior and lateral sides, or at alocation between the lateral and posterior sides, e.g., posterolateral.The stabilization apparatus 1400 may be used in one-level and two-levelspinal fixation or fusion procedures and is capable of being implantedin a minimally invasive technique. Analogously to the procedureillustrated in FIG. 31, the components of the dynamic stabilizationapparatus 1400 may be inserted through an access device, such as theexpandable conduit 20, into the operative space 90 defined at leastpartially by the skirt portion 24 of the expandable conduit 20. One ormore stabilization apparatuses 1400 may be used in the operative space90. As with the other devices for dynamic stabilization describedherein, the stabilization apparatus 1400 can be applied through theother access devices described herein or in connection with an open ormini-open procedure.

In one embodiment illustrated in FIG. 45, the dynamic stabilizationapparatus 1400 comprises a first fastener 1402 a and a second fastener1402 b. The first fastener 1402 a has a threaded shank 1404 a forengaging a portion of a vertebra V₁. The second fastener 1402 b has athreaded shank 1404 b for engaging a portion of a vertebra V₂. Thevertebrae V₁ and V₂ may be adjacent or may be separated by one or morevertebrae. The fasteners 1402 a and 1402 b each have enlarged heads inone embodiment (shown in FIGS. 48-49). The threaded shanks 1404 a, 1404b can take any suitable form, for example, including threads that areself-tapping and therefore can be advanced into a hole in a vertebra(e.g., a pedicle) that has not been pre-threaded. In some techniques,the threaded shanks 1404 a, 1404 b can be inserted into pedicle tunnelsthat have been pre-threaded. Also, although the dynamic stabilizationdevice 1400 includes fasteners 1402 a, 1402 b that have threaded shanks1404 a, 1404 b, other embodiments provide at least one fastener that canbe coupled with a vertebrae in another manner, for example, withoutrequiring threads.

The stabilization apparatus 1400 comprises a first housing 1406 a and asecond housing 1406 b. As shown in FIG. 45 and FIG. 52, each of thehousings 1406 a and 1406 b has a first passage 1407 a, 1407 b and asecond passage 1409 a, 1409 b with transversely oriented longitudinalaxes. The first fastener 1402 a extends through an opening 1411 a intothe second passage 1409 a of the housing 1406 a. Similarly, the secondfastener 1402 b extends through an opening 1411 b into the secondpassage 1409 b of the housing 1406 b.

The stabilization apparatus 1400 comprises a stabilization device thatpermits a range of motion of the spine under normal body loads. As shownin FIG. 45, the stabilization device may comprise a longitudinal member1408 that extends between the first housing 1406 a and the secondhousing 1406 b. In one embodiment, the longitudinal member 1408 extendsfrom the first housing 1406 a to the second housing 1406 b. As discussedbelow, the longitudinal member 1408 has a first end 1413 a (shown inFIG. 46) that is engaged in the first passage 1407 a of the firsthousing 1406 a and a second end 1413 b that is engaged in the firstpassage 1407 b of the second housing 1406 b. The length of thelongitudinal member 1408 between the first and second ends 1413 a, 1413b is sufficient to span the distance between the vertebrae V₁ and V₂,which can be adjacent vertebrae or spaced apart, as discussed above. Thelongitudinal member 1408 comprises an array of elongated, load-bearingelements. As used herein, an array of elements refers to an arrangementof one, two, three, four, or more elements. An array of elements may bearranged as a substantially linear array (e.g., generally as shown inFIGS. 45-46A), a substantially cylindrical array (e.g., generally asshown in FIGS. 46E-46J), or as an array having any other suitable shapeor configuration (e.g., as a rectangular array, an oval array, etc.).Elongated, load-bearing elements include, for example, sheets, plates,rods, or other suitable elongated members. The elongated load-bearingelements can have any suitable cross-sectional shapes, and differentload-bearing elements can have different cross-sectional shapes. Forexample, rods may have a cross-sectional shape that includes circularshapes, oval shapes, or rectangular shapes. The cross-sectional shape ofa load-bearing element can vary along its length (e.g., a rod may berectangular near one or both ends and circular near the center).

The longitudinal member 1408 shown in FIG. 45 comprises a substantiallylinear array that comprises a plurality of thin sheets 1410. Forexample, in one embodiment, the longitudinal member 1408 includes twothin sheets 1410. In another embodiment, the longitudinal member 1408includes more than two sheets, e.g., 10 or more, or as many as 12 ormore thin sheets 1410. The thin sheets 1410 may be configured as agenerally linear array of stacked sheets or layers (see, also, FIGS. 46and 46A). The number, configuration, and materials selected for thesheets 1410 can be selected to provide desirable performance, e.g.,rigidity and/or spring constant.

The stabilization apparatus 1400 comprises a first clamping device 1412a and a second clamping device 1412 b. The first clamping device 1412 ais coupled with the first housing 1406 a and is configured to secure aportion of the first end 1413 a of the longitudinal member 1408 to thefirst housing 1406 a. The second clamping device 1412 b is coupled withthe second housing 1406 b and configured to secure a portion of thesecond end 1413 b of the longitudinal member 1408 to the second housing1406 b while allowing the thin sheets 1410 to slide relative to eachother and relative to the second housing 1406 b.

In the embodiment shown in FIG. 45, the first clamping device 1412 a isconfigured to clamp the first end 1413 a of the longitudinal member1408. As used in this context, the phrase “to clamp” includes rigidlyconnecting a portion of the first end 1413 a of the longitudinal member1408 to the housing 1406 a whereby the thin sheets 1410 thereof have asubstantially limited or no range of motion relative to each other. Asdiscussed further below, in this embodiment the thin sheets 1410 may bemechanically coupled together at a portion of the end 1413 a to limittheir relative motion, for example, by the use of one or more rivets.

In other embodiments, the first clamping device 1412 a is configured tosecure a portion of the first end 1413 a of the longitudinal member 1408without clamping the first end 1413 a to the first housing 1406 a. Asused in this context, the phrase “to secure” includes connecting aportion of the first end 1413 a of the longitudinal member 1408 to thehousing 1406 a, but allowing at least some of the thin sheets 1410 toslide relative to each other and relative to the second housing 1406 a.In some embodiments, both ends 1413 a, 1413 b of the longitudinal member1408 are secured to the housings 1406 a, 1406 b without being clamped.In another embodiment, both ends of a longitudinal member similar to thelongitudinal member 1408 are clamped. In some variations where both endsof a longitudinal member are to be clamped, the longitudinal member ismade more flexible than the member 1408 because clamping both ends ofthe member significantly increases the stiffness compared to thestiffness of the dynamic stabilization apparatus 1400.

When the first and second ends 1413 a, 1413 b of the longitudinal member1408 are fastened as described, the longitudinal member 1408 acts as aspring. In some embodiments, the longitudinal member 1408 acts as a leafspring. In a dynamic spinal stabilization procedure, the distal ends ofthe fasteners 1402 a and 1402 b are coupled to two vertebrae V₁ and V₂.Movement of the vertebrae causes a change in the distance between thedistal ends of the fasteners 1402 a and 1402 b and the longitudinalmember 1408 flexes, permitting motion between the vertebrae butresisting the change in distance between the ends of the fasteners 1402a and 1402 b. The flexing of the longitudinal member 1408 is analogousto a spring, urging the fasteners 1402 a, 1402 b and the vertebrae V₁and V₂ back to a selected orientation, e.g., consistent with minimalspinal curvature. Accordingly, the dynamic stabilization apparatus 1400provides stability and restores natural stiffness to a diseased ordamaged portion of the spine.

The components of the dynamic stabilization apparatus 1400 can compriseany suitable material, such as a biocompatible metal, e.g., titanium ora titanium alloy. The components may also be fabricated from othermetals, or other suitable materials.

Although FIG. 45 illustrates a one-level treatment involving astabilization apparatus, another variation enables multilevelstabilization. A multilevel stabilization can be performed with alongitudinal member that is similar to the longitudinal member 1408,e.g., one that operates as a spring (e.g., a leaf spring) at least alonga portion of the member. The multilevel longitudinal member is longersuch that it can extend between three or more successive vertebrae. Themultilevel stabilization apparatus or the longitudinal member thereforecan be arranged to preserve at least some of the natural movement of thevertebrae with which it is coupled in a manner similar to the apparatus1400 and the member 1408.

In one variation, a multilevel stabilization apparatus is configured toapplied in different ways to different patients. For example, theapparatus can be configured such that an end of the multilevelstabilization member can be clamped or secured, as defined above,depending on the needs of the patient. The multilevel stabilizationmember can be further configured such that when two or more adjacentclamping devices clamp the member to two adjacent fasteners, theadjacent fasteners and the span of the member extending therebetween arevery rigid and provide a rigid fixation of the vertebrae with which theyare connected. The stabilization member can be further configured suchthat if one of two adjacent clamping devices is clamped while the otherof the two adjacent clamping devices is secured, the span of the membertherebetween acts as a spring and in certain embodiments as a leafspring. The multilevel stabilization apparatus is flexible in itsapplication in that it can be applied to rigidly fix two of threeadjacent vertebrae together (e.g., the caudal-most and a centralvertebrae) while permitting movement between one of the two fixedvertebrae and the third vertebrae (e.g., the cephalad-most and a centralvertebrae). In another technique, a multilevel procedure can involveclamping a central portion of a multilevel longitudinal member andsecuring peripheral portions, e.g., portions coupled with cephalad-mostand caudal-most screws of a multilevel stabilization apparatus. Themultilevel stabilization apparatuses can employ end caps, as discussedbelow in connection with FIG. 46A, to enable the multilevel longitudinalmember to be used in connection with standard fasteners and withfasteners with yokes, as discussed above.

FIG. 46 further illustrates features of an embodiment of the clampingdevices 1412 a and 1412 b and the longitudinal member 1408. The firstclamping device 1412 a clamps the first end 1413 a of the longitudinalmember 1408 in the second passage 1409 a, and the second clamping device1412 b secures the second end 1413 b of the member 1408 in the secondpassage 1409 b. The first clamping device 1412 a comprises a threadedportion 1416 configured to engage the housing 1406 a (shown in FIG. 45)and a yoke 1420 that is rotatably coupled with the threaded portion1416. Accordingly, the threaded portion 1416 can spin relative to theyoke 1420. The yoke 1420 is configured to engage the sides of thelongitudinal member 1408 as the threaded portion 1416 engages threadsformed in the housing 1406 a. A portion of the first end 1413 a of thelongitudinal member 1408 is clamped into the first housing 1406 a byscrewing the threaded portion 1416 into the housing 1406 a while theyoke 1420 engages the sides of the longitudinal member 1408. Thethreaded portion 1416 may be rotated relative to the yoke 1420 by usinga device such as the endoscopic screwdriver 660 (shown in FIG. 28). Arecess 1432 is provided in the threaded portion 1416 to allow theendoscopic screwdriver 660 or other similar device to engage and rotatethe threaded portion 1416. Other structures can be provided to spinningor rotating the threaded portion 1416.

The second clamping device 1412 b illustrated in FIG. 46 is similar tothe first clamping device 1412 a in one embodiment. The second clampingdevice 1412 b secures the second end of the longitudinal member 1408 tothe second housing 1406 b in a manner similar to that described for thefirst clamping device 1412 a. As discussed further below, a set ofretaining members 1424 and 1428 may be provided such that the thinsheets 1410 may slide relative to each other and relative to the secondhousing 1406 b.

In some embodiments, a position-limiting device 1429 is provided tolimit the range of positions at which the clamping device 1412 b cansecure the longitudinal member 1408. In one arrangement, theposition-limiting device 1429 is a ramp-like structure that has a lengththat is more than the length of the individual retaining members 1428.Because the length of the ramp exceeds that of the retaining members1428, the members 1424 on the clamping device 1412 b cannot couple withthe position-limiting device. Thus, the position limiting device 1429prevents the clamping devices 1412 b from being positioned too close tothe clamping device 1412 a.

In one arrangement, the longitudinal member 1408 is thinner (e.g., 0.005inches thinner) at the end without the rivets 1432. This arrangementpermits the clamping devices 1412 a, 1412 b to be interchangeable.

As discussed above, in some applications, it is desirable to contain anydebris that might be generated by the dynamic stabilization apparatus1400. One technique for limiting the spread of debris generated, e.g.,by wear of the apparatus 1400, is to provide a coating that reducesfriction or otherwise limits generation of particles or fragments fromthe apparatus 1400. The coating may be a conformal coating, e.g.,comprising a dielectric material selected to protect one or morecomponents of the apparatus 1400 from moisture, corrosion, abrasion, andother environmental stresses. Some conformal coatings that could be usedinclude silicone, acrylic, urethane, epoxy, and Parylene

The longitudinal member 1408 comprises a plurality of thin sheets 1410.In one embodiment, the thin sheets 1410 are fixed together at the firstend 1413 a of the longitudinal member 1408. The sheets 1410 may be fixedtogether by one or more rivets 1432 extending through some or all of thesheets. Two rivets 1432 are depicted in the embodiment shown in FIG. 46,although other numbers of rivets, including one, more than two, or nonecan be used. One of ordinary skill in the art will recognize that thethin sheets 1410 can be mechanically coupled together in other ways,such as by welding or with an adhesive. In some embodiments, the thinsheets 1410 are mechanically coupled together by the pressure exerted onthe end portion 1413 a by the first clamping device 1412 a while it isfirmly secured to the housing 1406 a.

The second clamping device 1412 b may comprise a first retaining member1424, and the longitudinal member 1408 may comprise a second retainingmember 1428. The first and second retaining members 1424, 1428 areconfigured to limit the longitudinal motion of the longitudinal member1408 while allowing at least some of the thin sheets 1410 to sliderelative to each other. In the embodiment shown in FIG. 46, theretaining members 1424, 1428 comprise a plurality of notches configuredto mate with each other and to allow the second end of the longitudinalmember 1408 to be secured by the second clamping device 1412 b withoutclamping the thin sheets 1410 together. In some embodiments, fewernotches than shown can be provided. For example, a single notch may beused in the retaining members 1424, 1428. In other embodiments 8 to 10or more notches may be provided to limit the motion of the longitudinalmember 1408. The notches in the retaining member 1428 may be provided onone or more of the thin sheets 1410 of the longitudinal member 1408. Itwill be apparent to one of ordinary skill in the art that the retainingmembers 1424, 1428 may take alternative forms. For example, a pin on thebottom of the threaded portion 1416 may be configured to engage a grooveor dimple on the upper surface of the proximal-most sheet 1410 of thelongitudinal member 1408 in order to limit its motion. Alternatively,the first passage 1407 b of the second housing 1406 b may be configuredto prevent one or more of the thin sheets 1410 from extending throughthe second housing 1406 b while allowing other thin sheets 1410 toextend therethrough.

The first clamping device 1412 a shown in FIG. 46 is similar to thesecond clamping device 1412 b in one embodiment. In embodiments in whichthe first end 1413 a of the longitudinal member 1408 is clamped ratherthan secured to the first housing 1406 a, the first clamping member 1412a may be configured without the retaining member 1424.

By fastening the first and second ends 1413 a, 1413 b of thelongitudinal member 1408 as described, the motion of the longitudinalmember 1408 in a direction parallel to its longitudinal axis of themember 1408 is limited while the sliding of the thin sheets 1410 allowsthe member 1408 to flex, for example, at least partially in thetransverse direction. Accordingly, this embodiment of the longitudinalmember 1408 acts as a leaf spring. The characteristics of the spring,such as its spring rate, can be selected by appropriately selecting thenumber, the length and thickness, and the material properties of thethin sheets 1410. Accordingly, different embodiments of the longitudinalmember 1408 may comprise a linear spring rate or a nonlinear springrate.

Each of the thin sheets 1410 of the longitudinal member 1408 may befabricated from a different material. To limit the extensibility of thelongitudinal member 1408, some of the thin sheets 1410 may be fabricatedfrom a material substantially incompressible or substantiallyinextensible along the longitudinal axis of the member 1408 under loadsprovided in normal spinal motion. Suitable materials include abiocompatible metal, e.g., titanium or a titanium alloy. The thin sheets1410 may also be fabricated from other metals, or other suitablematerials.

The operation of the longitudinal member 1408 may be facilitated byconfiguring the member 1408 to minimize wear, for example, to configurethe thin sheets 1410 to promote sliding thereof. Wear may be minimizedby, for example, coating the sheets 1410 with low-friction material. Oneembodiment of the longitudinal member 1408 comprises thin sheets 1410made from at least two materials. One material may be substantiallyincompressible or inextensible along its longitudinal axis, such as, forexample, a biocompatible material like titanium or titanium alloy. Theother material may be a low-friction material to minimize wear and topromote sliding of the thin sheets 1410. Suitable low-friction materialsinclude, for example, ultra high molecular weight polyethylene (UHMWPE)or nylon. In the embodiment shown in FIG. 46, sheets of anincompressible material are alternated with sheets of a low-frictionmaterial to minimize wear and promote sliding. Some of the arrangementsthat reduce friction and promote sliding also substantially preventgeneration of loose debris that might otherwise result from relativemotion of the sheets 1410.

FIG. 46A illustrates one variation of a longitudinal member 1408′ thatpermits the use of a conventional fastener, such as a conventionalpedicle screw with a housing and cap screw arrangement, similar to thosedisclosed in, for example, U.S. patent application Ser. No. 11/490,511,filed Jul. 20, 2006, entitled “APPARATUS FOR CONNECTING A LONGITUDINALMEMBER TO A BONE PORTION,” and U.S. patent application Ser. No.10/483,605, filed Jan. 13, 2004, entitled “APPARATUS FOR CONNECTING ALONGITUDINAL MEMBER TO A BONE PORTION,” each of which is herebyincorporated by reference herein in its entirety.

The longitudinal member 1408′ is similar to the longitudinal member 1408except as set forth below. The longitudinal member 1408′ has first andsecond ends 1413 a′, 1413 b′ and a plurality of laminations or thinsheets 1410′ extending therebetween. The thin sheets 1410′ areconfigured in a generally linear array of laminations. The thin sheets1410′ and the longitudinal member 1408′ act as a leaf spring in use, asdiscussed further below. The longitudinal member also includes a firstend cap 1415 a′ and a second end cap 1415 b′. The first end cap 1415 a′is located adjacent to the first end 1413 a′ of the longitudinal member1408′ and houses one end of the thin sheets 1410′. The second end cap1415 b′ is located adjacent to the second end 1413 b′ of thelongitudinal member 1408′ and houses the other end of the thin sheets1410′ in one embodiment.

Preferably at least one of the two end caps is coupled with acorresponding end portion of the thin sheets 1410′ in a manner thatpermits the sheets to move relative to each other, similar to themovement of the thin sheets 1410. For example, a first rivetedconnection 1417 a′ can be provided between the first end cap 1415 a′ andthe thin sheets 1410′ adjacent to the first end 1413 a′. The firstriveted connection 1417 a′ can include two rivets. The first rivetedconnection 1417 a′ is a rigid connection in one arrangement thatsubstantially prevents sliding of the thin sheets 1410′ relative to eachother adjacent to the first end 1413 a′. A second riveted 1417 b′connection can be provided between the second end cap 1415 b′ and thethin sheets 1410′ adjacent to the second end 1413 b′. The second rivetedconnection 1417 b′ can include one or more slots 1418′ formed in thethin sheets 1410′ and corresponding rivet holes 1419′ formed in thesecond end cap 1415 b′. One or a plurality, e.g., two, rivets can beextended through the rivet holes 1419′ and into the slots 1418′. Wheninstalled in the rivet holes 1419′ and the slots 1418′ the rivet(s)permit movement of the thin sheets 1410′ in a manner similar to a leafspring as discussed above.

The longitudinal member 1408′ is advantageous in that the end caps 1415a′, 1415 b′ absorb the force of conventional cap screws or other similarclamping devices while permitting the leaf-spring-like movement of thethin sheets 1410′. This enables the longitudinal member 1408′ to be usedwith a wide array of standard, as well as propriety, fasteners,including screws configured for insertion into pedicles or other bonysegments.

FIG. 46B is a perspective view schematically illustrating anotherembodiment of a dynamic stabilization apparatus 1400 a that comprises afirst fastener 1402 a, a second fastener 1402 b, and a longitudinalmember 1408 a. The first fastener 1402 a has a threaded shank 1404 a forengaging a portion of a vertebra V₁. The second fastener 1402 b has athreaded shank 1404 b for engaging a portion of a vertebra V₂. Thevertebrae V₁ and V₂ may be adjacent or may be separated by one or morevertebrae. The fasteners 1402 a and 1402 b comprise housings 1406 a and1406 b, respectively. Cap screws 1438 a and 1438 b may be used to secureends of the longitudinal member 1408 a to the fasteners 1402 a and 1402b, respectively. The fasteners 1402 a and 1402 b may be standard pediclescrews or bone anchors such as the fastener 600 illustrated in FIGS. 26and 27. In some embodiments, at least one of the fasteners 1402 a and1402 b is positionable in any one of a plurality of angular positionsrelative to the housing 1406 a or 1406 b, respectively, as furtherdescribed below. FIGS. 46C and 46D, respectively, are side and top planviews of the dynamic stabilization apparatus 1400 a.

FIG. 46E is a side cross-section view of the dynamic stabilizationapparatus 1400 a taken along section plane 46E-46E of FIG. 46D. Thelongitudinal member 1408 a comprises retention members 1442 a and 1442b, an elongated central core 1440, and a plurality of narrow rods 1450arranged in a generally cylindrical array surrounding the central core1440 (best seen in FIGS. 46F and 46G). Each retention member 1442 a,1442 b has a longitudinal passageway 1462 a, 1462 b (see FIG. 46F)having a cross-sectional area sufficiently large for ends 1454 a, 1454 bof the central core 1440 to pass therethrough. Opposing ends of thenarrow rods 1450 engage the retention members 1442 a, 1442 b,respectively, and in one embodiment are configured in a substantiallycylindrical, cage-like array. As depicted, the rods 1450 have generallycircular cross-sectional shapes, but in other embodiments the rods 1450may have different cross-sectional shapes (e.g., oval, rectangular,flattened, etc.).

End caps 1448 a, 1448 b secure the retention members 1442 a, 1442 b tothe ends 1454 a, 1454 b of the central core 1440, respectively. The core1440 and the rods 1450 may be configured so that the longitudinal member1408 a resists axial compression but permits a degree of transverseflexibility when subjected to spinal loads. For example, the number ofthe rods 1450, their flexibility, as well as the flexibility of the core1440, can be selected to provide a desired range of motion for the spineof a patient. Embodiments of the longitudinal member 1408 aadvantageously can flex in multiple directions, for example, insubstantially all directions that are substantially transverse to theelongated core member 1440. Accordingly, the longitudinal member 1408 abeneficially provides dynamic spinal stabilization not only for forcescorresponding to spinal flexion and compression but also for forcescorresponding to lateral or transverse displacements of the spinal.Further details of embodiments of the longitudinal member 1408 a areprovided below.

The longitudinal member 1408 a may be attached to the fasteners 1402 a,1402 b by inserting ends of the member 1408 a into the housings 1406 a,1406 b and securing the cap screws 1438 a, 1438 b, respectively. Thelength of the longitudinal member 1408 a between the first and secondends 1454 a and 1454 b is sufficient to span the distance between thevertebrae V₁ and V₂, which can be adjacent vertebrae or spaced apart.The longitudinal member 1408 a may be sufficiently flexible to providedynamic stability to portions of the spine near the vertebrae V₁ and V₂.

FIG. 46F is an exploded perspective view of one embodiment of thelongitudinal member 1408 a. The core 1440 is an elongated elementextending between the ends 1454 a and 1454 b. The core 1440 has twoflanges 1444 a and 1444 b defining a central portion 1441 therebetween.The core 1440 may be fabricated as an integral unit or as separatepieces that are thereafter joined. The core 1440 may be made from amaterial that flexes under normal spinal loads. In some embodiments, thecentral portion 1441 comprises a different cross-sectional area,cross-sectional shape, and/or material than portions near the ends 1454a, 1454 b. For example, the ends 1454 a, 1454 b may be made from asubstantially rigid material (e.g., titanium), while the central portion1441 is made from an elastomeric material (e.g., a polymer). In theembodiment shown in FIG. 46F, the central portion 1441 is a flexiblerod. In other embodiments, the central portion 1441 may be configured inpart as a flexible tether, braided fabric, spring, and/orball-and-socket linkage. Compressible O-rings 1446 a and 1446 b aredisposed adjacent the flanges 1444 a and 1444 b, respectively, andpermit a degree of longitudinal compression of the member 1408 a asfurther described below. The O-rings 1446 a, 1446 b may be made from anysuitable elastomeric material.

The retention members 1442 a, 1442 b have substantially central,longitudinal passageways 1462 a, 1462 b, respectively, having across-section sufficient to permit the ends 1454 a, 1454 b of the core1440, respectively, to pass therethrough. In the embodiment shown inFIG. 46F, each retention member 1442 a, 1442 b comprises a lateralportion 1443 a, 1443 b and a medial portion 1445 a, 1445 b,respectively, which are substantially cylindrical in shape. The medialpotions 1445 a, 1445 b have larger cross sectional areas than thelateral portions 1443 a, 1443 b, although this is not a requirement.Likewise, the cross-sectional area of the passageways 1462 a, 1462 b maybe larger within the medial portions 1445 a, 1445 b than within thelateral portions 1443 a, 1443 b. The retention members 1442 a, 1442 bmay be made from a substantially rigid biocompatible material such astitanium or a titanium alloy.

In the embodiment shown in FIG. 46F, each of the medial portions 1445 a,1445 b comprises openings 1452 a, 1452 b configured to receive oppositeends of the rods 1450. The openings 1452 a, 1452 b extend substantiallyparallel to the longitudinal passageways 1462 a, 1462 b, so that therods 1450 are maintained substantially parallel to the elongated core1440, In certain embodiments, the openings 1452 a, 1452 b in the medialportions 1445 a, 1445 b are spaced in a substantially uniform azimuthalmanner around the respective longitudinal passageways 1462 a, 1462 b.Accordingly, when opposing ends of the rods 1450 are disposed in theopenings 1452 a, 1452 b, respectively, the rods 1450 will form asubstantially cylindrical, cage-like array, which surrounds theelongated core 1440 (see FIGS. 46F and 46G). In other embodiments, thearray of rods 1450 (as viewed perpendicularly to the longitudinal axisof the member 1408 a) may be configured in a linear array, an ovalarray, a rectangular array, or any other suitably shaped array. Manyvariations are contemplated.

The number of openings 1452 a, 1452 may be equal to the number of rods1450 used in the longitudinal member 1408 a. In some embodiments, themedial portions 1445 a, 1445 b may be fabricated with a relatively largenumber of openings 1452 a, 1452 b (e.g., generally as shown in FIG.46F). Rods 1450 may be placed in all, or fewer than all, of the openings1452 a, 1452 b. Additionally, in embodiments using fewer rods 1450 thanopenings 1452 a, 1452 b, individual rods 1450 can be disposed atselected azimuthal positions surrounding the core 1440 to provide anappropriate range of spinal flexibility for the patient.

Generally, each of the rods 1450 used in the longitudinal member 1450 ismade from the same material, but this is not a requirement. Each rod1450 may be made from a material that resists axial compression butwhich permits a degree of transverse flexibility. The transversecross-sectional shape, area, length, or diameter of the rods 1450 mayalso be selected to provide suitable axial inflexibility and transverseflexibility. In some embodiments, the rods 1450 are made from abiocompatible material such as titanium, a titanium alloy, or stainlesssteel.

FIG. 46G shows an embodiment of the longitudinal member 1408 a in anassembled state. Opposing ends of the rods 1450 are disposed in theopenings 1452 a, 1452 b of the retention members 1442 a, 1442 b,respectively. The retention members 1442 a, 1442 b engage the core 1440so that the O-rings 1446 a, 1446 b abut inner surfaces of the medialportions 1445 a, 1445 b, respectively. In some embodiments, the ends1454 a, 1454 b extend entirely through the passageways 1452 a, 1452 b,which permits the retention members 1442 a, 1442 b to be secured to thecore member 1400 by the end caps 1448 a, 1448 b. In various embodiments,the end caps 1448 a, 1448 b are threaded and/or welded to the core 1440.In other embodiments, adhesives are used. As shown in FIG. 46F, notchesor grooves 1465 a, 1465 b may be formed in the ends 1454 a, 1454 b,respectively, to permit the end caps 1448 a, 1448 b to be snap-fit ontothe core 1440. In some embodiments, a combination of these techniquesmay be used.

The longitudinal member 1408 a can be configured so that there is an endspace 1462 (best seen in FIG. 46E) in the openings 1452 a and/or 1452 bin the retention members 1442 a and/or 1442 b. The end space 1462 maypermit relatively small ranges of extension and/or retraction of therods 1450 in the openings 1452 a and/or 1452 b or relative movementbetween the rods 1450 and the retention members 1442 a, 1442 b when thelongitudinal member 1408 a is flexed, compressed, and/or extended. Insome embodiments, the range of longitudinal retraction of the member1408 a is limited in part by the length of the end space 1462, becauseat a limiting value of the retraction, ends of the rods 1450 in the endspace 1462 will contact the bottom of the openings, thereby preventingfurther retraction. The length of the end space 1462 is determined by,for example, the depth of the openings 1452 a, 1452 b, the length of therods 1450, and the spacing between of the retention members 1442 a, 1442b. Additionally, the length of the end space 1462 can be configured topermit the longitudinal member 1408 a to be slightly compressible in anaxial direction generally parallel to the elongated care 1440. Forexample, if a compressive load is applied to opposing ends of thelongitudinal member 1408 a, the O-rings 1446 a, 1446 b will compress,and ends of the rods 1450 will slide into the end space 1462, therebypermitting the retention members 1442 a and 1442 b to move toward eachother. Accordingly, in certain embodiments, the longitudinal member 1408a is relatively inflexible along its longitudinal axis but may beconfigured to retain a limited range of longitudinal motion under spinalforces of compression or tension.

In some embodiments, an optional outer sheath 1460 is used to cover acentral portion 1462 of the longitudinal member 1408 a. The outer sheath1460 may comprise a cylindrical piece of heat-shrink tubing or othersuitable protective covering. The outer sheath 1460 can be left on thelongitudinal member 1408 a after delivery to the surgical site toprevent tissue growth into the array of rods 1450. In some surgicalapplications, the outer sheath 1460 is removed after the longitudinalmember 1408 a is inserted into the patient. The outer sheath 1460 isillustrated in FIGS. 46E and 46F but is removed for clarity in FIG. 46G.

FIGS. 46H and 46I are perspective views schematically illustratingadditional embodiments of the longitudinal member 1408 a. In theseembodiments, a substantially cylindrical, cage-like array of rods 1450is secured between two substantially cylindrical retention members 1442a and 1442 b. In these embodiments, an elongated core 1440 may bedisposed substantially symmetrically within the array of rods 1450 andmay also extend between the retention members 1442 a, 1442 b. The core1440 may be secured to the retention members 1442 a, 1442 b by, e.g.,welding and/or adhesives. As described above, the rods 1450 and theoptional core 1440 may be fabricated from a material that permitsembodiments of the longitudinal member 1408 a to be relativelyinflexible in directions along the longitudinal axis of the member 1408a and to be relatively flexible in directions generally transverse tothe longitudinal axis of the member 1408 a.

As can be seen in FIGS. 46H and 46I, ends of the rods 1450 and the core1440 may extend through openings in the retention members 1442 a, 1442b, which may permit their easier arrangement in and attachment to thelongitudinal member 1408 a. The rods 1450 and the optional core 1440 maybe attached to the retention members 1442 a, 1442 b by, for example,welding and/or adhesives. End caps generally similar to those describedabove are used in some embodiments. In certain embodiments, the core1440 is secured (e.g., clamped) to both of the retention members 1442 a,1442 b, while some or all of the rods 1450 are secured to a retentionmember at one end of the longitudinal member 1408 a but are allowed toslide through the openings in the retention member at the opposing endof the longitudinal member 1408 a. Such embodiments advantageouslypermit the undamped ends of the rods to slide relative to the retentionmember as the longitudinal member 1408 a flexes.

Some embodiments of the longitudinal member 1408 a comprise an optionalsheath 1460 covering the rods 1450; for example, as shown in FIG. 46I.The outer sheath 1460 can be left on the longitudinal member 1408 aafter delivery to the surgical site to prevent tissue growth into thearray of rods 1450. In some surgical applications, the outer sheath 1460is removed after the longitudinal member 1408 a is inserted into thepatient.

FIG. 46J is a perspective view of another embodiment of a longitudinalmember 1408 a′ comprising an array of rods 1450′ extending between tworetention members 1442 a′ and 1442 b′. The array of rods 1450′ may beconfigured in a substantially cylindrical, cage-like configuration(e.g., substantially as shown in FIG. 46J), and in some embodiments, thearray includes a rod disposed along a substantially central,longitudinal axis of the member 1408 a′. The rods 1450′ may be formedfrom a material that resists axial compression (e.g., is relativelyinflexible axially), but that permits a range of transverse deflection(e.g., is relatively flexible transversely). In some embodiments, therods 1450′ are made from a biocompatible metal such as titanium. Theretention members 1442 a′ and 1442 b′ may be generally sphericallyshaped and may include substantially planar portions 1470 a′ and 1470b′, respectively. The planar portions 1470 a′ and 1470 b′ may permit thecap screws 1438 a and 1438 b to more securely couple the retentionmembers 1442 a′ and 1442 b′ to the fasteners 1402 a and 1402 b. Asdescribed above with reference to FIG. 46H, in some embodiments, ends ofsome of the rods 1450′ are clamped by one retention member (e.g., theretention member 1442 a′) while opposing ends of these rods 1450′ areconfigured to slide relative to the other retention member (e.g., theretention member 1442 b′). In such embodiments, the array of rods 1450′may include a central rod that is secured to the retention members 1442a′ and 1442 b′. Such embodiments advantageously permit some of the rods1450′ to slide relative to the undamped retention member (e.g., themember 1442 b′) when the longitudinal member 1408 a′ flexes. Someembodiments of the longitudinal member 1408 a′ may include an outersheath surrounding the array of rods 1450′ (not shown in FIG. 46J). Insome embodiments, an outer sheath (not shown in FIG. 46J) is used tocover the array of rods 1450′. The outer sheath can be is left on thelongitudinal member 1408 a′ after delivery to the surgical site toprevent tissue growth into the array of rods 1450′. In some surgicalapplications, the outer sheath is removed after the longitudinal member1408 a′ is inserted into the patient.

The longitudinal member 1408 a, 1408 a′ man be configured to act like aspring (e.g., similar to a leaf spring) as further described below. Thelongitudinal member 1408 a, 1408 a′ may be configured to have a springrate (e.g., stiffness) that provides a desired degree of dynamicstabilization and range of motion. Embodiments of the longitudinalmember 1408 a, 1408 a′ can be configured with a linear spring rate or anonlinear spring rate. In certain embodiments, the longitudinal member1408 a, 1408 a′ is also configured to act as a spring along thelongitudinal axis of the member 1408 a, 1408 a′. In certain suchembodiments, the spring rate along the longitudinal direction is largerthan the spring rate along a transverse direction (e.g., the member 1408a, 1408 a′ is suffer longitudinally than transversely).

FIGS. 47-54 illustrate the operation of one embodiment of the dynamicstabilization apparatus 1400. Each of the fasteners 1402 a and 1402 bhas a threaded shank 1404 a and 1404 b and an enlarged head 1436 a and1436 b, respectively. Each of the housings 1406 a, 1406 b has a firstpassage 1407 a, 1407 b and a second passage 1409 a, 1409 b that has alongitudinal axis extending transverse to the first passage 1407 a, 1407b. The fasteners 1402 a and 1402 b extend through an opening in thesecond passage 1409 a, 1409 b of the corresponding housings 1406 a and1406 b. In one embodiment of the dynamic stabilization apparatus 1400,at least one of the fasteners 1402 a and 1402 b is positionable in anyone of a plurality of angular positions relative to the longitudinalaxis of the second passage 1409 a, 1409 b of the corresponding housing1406 a or 1406 b. Arrangements that facilitate such positioning and thatcan be used in connection with any of the members 1408, 1408′, or 1408 aare described in, for example, U.S. patent application Ser. No.11/490,511, filed Jul. 20, 2006, entitled “APPARATUS FOR CONNECTING ALONGITUDINAL MEMBER TO A BONE PORTION,” and U.S. patent application Ser.No. 10/483,605, filed Jan. 13, 2004, entitled “APPARATUS FOR CONNECTINGA LONGITUDINAL MEMBER TO A BONE PORTION,” each of which is herebyincorporated by reference herein in its entirety.

FIGS. 50-52 illustrate a configuration of the dynamic stabilizationapparatus 1400 of FIG. 45 when the vertebrae V₁ and V₂ are in extension.The vertebrae V₁ and V₂ exert extension forces F_(E) on the distal endsof the fasteners 1402 a and 1402 b, which causes the distal ends toseparate from each other. As shown in FIG. 52, the thin sheets 1410 ofthe longitudinal member 1408 flex transversely to the longitudinal axisof the member 1408. When undergoing spinal extension, the shape of thelongitudinal member 1408 becomes concave in the direction away from thespine (upward in FIG. 52), because the first end of the longitudinalmember 1400 is clamped by the first housing 1406 a while the second endof the longitudinal member 1408 permits the thin sheets 1410 to sliderelative to each other and relative to the second housing 1406 b.Accordingly, the longitudinal member 1408 acts like a leaf spring andexerts a restoring force that tends to resist the extension of thevertebrae V₁ and V₂.

FIGS. 53-54 illustrate a configuration of the dynamic stabilizationapparatus 1400 when the vertebrae V₁ and V₂ are in flexion. Thevertebrae V₁ and V₂ exert flexion forces F_(F) on the distal ends of thefasteners 1402 a and 1402 b, which causes the distal ends to approacheach other. As shown in FIG. 54, the thin sheets 1410 of thelongitudinal member 1408 flex transversely to the longitudinal axis ofthe member 1408. When undergoing spinal flexion, the shape of thelongitudinal member 1408 becomes concave in the direction toward thespine (downward in FIG. 54), because the first end of the longitudinalmember 1400 is clamped by the first housing 1406 a while the second endof the longitudinal member 1408 permits the thin sheets 1410 to sliderelative to each other and relative to the second housing 1406 b.Accordingly, the longitudinal member 1408 acts like a leaf spring andexerts a restoring force that tends to resist the flexion of thevertebrae V₁ and V₂.

In other embodiments of the dynamic stabilization apparatus 1400, thenumber, the length and thickness, and the material properties of thethin sheets 1410 (or 1410′) can be selected such that the longitudinalmember 1408 (or 1408′) exhibits a leaf spring restoring force havingpredetermined characteristics to resist flexion or extension of thevertebrae V₁ and V₂. For example, in one embodiment the restoring forcemay be directly proportional to the transverse deformation of thelongitudinal member 1408 (or 1408′), e.g., with a linear spring rate,according to Hooke's law. In other embodiments, the restoring force canbe a nonlinear function of the transverse deformation of thelongitudinal member 1408 (or 1408′), e.g., exhibiting a nonlinear springrate. In such a manner, the transverse stiffness of the longitudinalmember 1408 (or 1408′) may be predetermined to achieve the appropriateamount of dynamic stabilization of the spine.

The dynamic stabilization apparatus 1400 a can also be configured sothat the longitudinal member 1408 a (or 1408 a′) exhibits desiredstabilization properties under spinal loads. For example, the elasticproperties of the core 1440 as well as the number, the length and thediameter, and the material properties of the array of rods 1450 (or1450′) can be selected so that the longitudinal member 1408 a (or 1408a′) acts as a spring with a restoring force having predeterminedcharacteristics to resist flexion or extension of the vertebrae V₁ andV₂. Embodiments of the longitudinal members 1408 a and 1408 a′ may beconfigured to exhibit a linear spring rate or a nonlinear spring rate.In certain embodiments, the longitudinal member 1408 a (or 1408 a′) actsas a spring along the longitudinal direction and along one or moretransverse directions. In certain such embodiments, the spring ratealong the longitudinal direction is larger than the spring rate along atransverse direction (e.g., the member 1408 a or 1408 a′ is stifferlongitudinally than transversely).

In certain embodiments, the longitudinal member 1408 a (or 1408 a′) maybe configured so that it is relatively inflexible along its longitudinalaxis in order to provide suitable support between vertebrae. Thelongitudinal member 1408 a (or 1408 a′) may be configured to have adesired range of longitudinal flexibility under compressive or tensileloads by suitably selecting, for example, elastomeric properties of theO-rings 1446 a, 1446 b, the length of the end space 1462, thelongitudinal compressibility of the core 1440 and/or the rods 1450, etc.In some embodiments, the longitudinal member 1408 a (or 1408 a′) isrelatively flexible in directions generally transverse to thelongitudinal axis of the member 1408 a (or 1408 a′). The longitudinalmember 1408 a (or 1408 a′) may be configured to have a range oftransverse flexibility by selecting, for example, the transverseflexibility of the core 1440 and the rods 1450, the length of the endspace 1462, etc. In certain embodiments, the longitudinal member 1408 a(or 1408 a′) is relatively more flexible in one (or more) transversedirections than in the longitudinal direction.

Additionally, an advantage of certain embodiments of the longitudinalmembers 1408 a and 1408 a′ is that they can be configured to exhibitflexibility in multiple dimensions. For example, the longitudinalmembers 1408 a, 1408 a′ shown in FIGS. 46B-46J are capable of flexing inany direction substantially transverse to the longitudinal axis of themembers 1408 a, 1408 a′. Accordingly, the longitudinal members 1408 a,1408 a′ can be configured to provide dynamic stabilization not onlyunder forces of spinal flexion and compression (e.g., similarly as shownin FIGS. 52 and 54), but also under spinal forces acting generallytransverse to the spinal axis.

The foregoing structures are useful for stabilizing at least twovertebrae of the spine of a patient. An embodiment comprises coupling afirst screw with a vertebra, the first screw having a first housing. Asecond screw having a second housing is coupled with another vertebra. Afirst end of a multi-layered longitudinal member is secured with thefirst screw. A second end of the multi-layered longitudinal member issecured with the second screw while allowing relative motion between thelayers of the longitudinal member.

In other techniques, a first cap screw is secured onto the first end ofthe longitudinal member to secure the longitudinal member in the firsthousing. A second cap screw is secured on the second end of thelongitudinal member to secure the second end of the longitudinal memberin the second housing while allowing relative motion between the secondend of the longitudinal member and the second housing. In someembodiments, the cap screw comprises a threaded portion configured toengage the housing and a yoke that is rotatably coupled with thethreaded portion and configured to engage the longitudinal member.

In other variations, the layers of the longitudinal member may comprisedifferent materials, including, for example, titanium, titanium alloys,or other biocompatible materials. In some embodiments, the longitudinalmember comprises a low friction material that is used to promote slidingbetween the layers and to reduce wear and to substantially preventgeneration of loose debris due to the relative motion within the member.A suitable low-friction material includes ultra high molecular weightpolyethylene (UHMWPE). In some embodiments, the longitudinal member haslayers that alternate in composition. For example, in one embodiment thelayers alternate between titanium and UHMWPE.

In some embodiments, one or both ends of the longitudinal member may besecured to the housings such that the layers may slide relative to eachother and relative to the housings. In other embodiments, at least oneend of the longitudinal member may be clamped to the housing such thatmotion of the layers relative to each other and relative to the housingis minimized. In such embodiments, the layers toward at least one end ofthe longitudinal member may be mechanically coupled together to preventtheir relative motion, for example, by the use of rivets, welds, oradhesives.

The spinal stabilization apparatus may comprise retention members thatlimit the longitudinal motion of an end of the longitudinal member whileallowing the layers to slide relative to each other and relative to thehousing. In some embodiments, the retention members may comprise a setof notches on the longitudinal member that are mated to a set of notcheson the housing or on the cap screw. The set of notches may be disposedon one or more layers of the longitudinal member.

By coupling the multi-layered longitudinal member to the vertebrae asdescribed, the longitudinal member acts as a leaf spring that resistsextension and flexion of the vertebrae to which the stabilization deviceis coupled, thereby imparting stability and natural stiffness to adiseased or damaged portion of the spine. The characteristics of theleaf spring such as its spring rate and stiffness may be chosen byappropriately selecting the number, the length and thickness, and thematerial properties of the layers. The spring rate may be linear ornonlinear.

Analogously to the procedure illustrated in FIG. 31, the spinalstabilization apparatus comprising the screws, the longitudinal member,the housings, and the cap screws may be inserted through an accessdevice, such as the expandable conduit 20, into the operative space 90defined at least partially by the skirt portion 24 of the expandableconduit 20.

Many variants of the method and apparatuses described above will beclear from the application. For example, the spinal stabilizationapparatus may be coupled to the vertebrae with conventional pediclescrews or the fastener 600, described above. Also, the longitudinalmember may be secured or clamped to the housings by use of theendoscopic screwdriver 660 or other similar device.

F. Stabilization Device Made from Flexible Material

FIG. 55 illustrates another embodiment of a stabilization device 1550.In one embodiment, the stabilization device 1550 is configured to besecured to the posterior side of the spine. However, the device 1550 maybe modified for use on the anterior or lateral sides of the spine, or ata location between the anterior and lateral sides, or at a locationbetween the lateral and posterior sides, e.g., posterolateral.

In this embodiment of a stabilization device 1550, flexible implants1554 are anchored to the adjacent vertebrae V1, V2 and V3. The implants1554 preferably have a low profile and are conformable to the spinalanatomy to minimize intrusion into the surrounding tissue andvasculature. The implants 1554 attach to vertebrae and preventseparation of the vertebrae while allowing normal extension andarticulation of the spinal column segment. Portions of the implants 1554and the fasteners 1558 attaching the implant 1554 to vertebrae can be atleast partially or fully embedded within the vertebrae to minimizeintrusion into the surrounding tissue and vasculature.

It is contemplated that the flexible implants 1554 of the stabilizationdevice 1550 described herein can be made from resorbable material,nonresorbable material and combinations thereof. In one example,resorbable implants 1554 can be used with interbody fusion devices sincea permanent exterior stabilization may not be desired after fusion ofthe vertebrae. It is also contemplated that the fasteners 1558 used toattach the implants 1554 to the vertebrae can be made from resorbablematerial, nonresorbable material, and combinations thereof.

The implants 1554 can be flexible, tear resistant, and/or suturable. Theflexible implant 1554 can also be fabricated from synthetic flexiblematerials in the form of fabrics, non-woven structures, two or threedimensional woven structures, braided structures, and chainedstructures. The implants 1554 can also be fabricated fromnatural/biological materials, such as autograft or allograft, taken frompatellar bone-tendon-bone, hamstring tendons, quadriceps tendons, orAchilles tendons, for example. Growth factors or cells can beincorporated into the implants 1554 for bone ingrowth and bonyattachment or for soft tissue ingrowth. Possible growth factors that canbe incorporated include transforming growth factor pi, insulin-likegrowth factor 1, platelet-derived growth factor, fibroblast growthfactor, bone morphogenetic protein, LIM mineralization protein (LMP),and combinations thereof.

Possible implant materials include synthetic resorbable materials suchas polylactide, polyglycolide, tyrosine-derived polycarbonate,polyanhydride, polyorthoester, polyphosphazene, calcium phosphate,hydroxyapatite, bioactive glass and combinations thereof. Possibleimplant materials also include natural resorbable materials such asautograft, allograft, xenograft, soft tissues, connective tissues,demineralized bone matrix, and combinations thereof. Possible implantmaterial further include nonresorbable materials such as polyethylene,polyester, polyvinyl alcohol, polyacrylonitrile, polyamide,polytetrafluorethylene, poly-paraphenylene terephthalamide, cellulose,shape-memory alloys, titanium, titanium alloys, stainless steel, andcombinations thereof.

The stabilization device 1550 described herein includes fasteners 1558to attach the implant 1554 to the vertebrae. It is contemplated that thefasteners 1558 can be, for example, interference screws or anchors, gullanchors, suture anchors, pin fasteners, bone screws with spiked washers,staples, buttons, or bone screws such as the fastener 600 describedabove. It is contemplated that the fasteners 1558 can be made fromresorbable materials, nonresorbable materials, and combinations thereof.Possible synthetic resorbable materials include polylactide,polyglycolide, tyrosine-derived polycarbonate, polyanhydride,polyorthoester, polyphosphazene, calcium phosphate, hydroxyapatite,bioactive glass, and combinations thereof. Possible natural resorbablematerials include cortical bone, autograft, allograft, and xenograft.Possible nonresorbable materials include carbon-reinforced polymercomposites, shape-memory alloys, titanium, titanium alloys, cobaltchrome alloys, stainless steel, and combinations thereof.

Referring now to FIG. 55, the stabilization device 1550 includes aflexible implant 1554 that extends along the posterior faces ofvertebrae V1, V2 and V3, and is attached to a first vertebra V1 and asecond vertebra V3. The flexible implant 1554 may be configured toresist extension, flexion, and/or lateral bending loads created bymotion of the spinal column depending on the location or locations ofthe spinal column segment on which the implant 1554 is positioned.

In one embodiment, the flexible implant 1554 has a first end 1554 a andan opposite second end 1554 b. Vertebra V1 includes a first opening onits posterior face and a first tunnel extending therefrom. Vertebra V3has a second opening on its posterior face and a second runnel extendingtherefrom. The ends 1554 a and 1554 b are inserted into respective onesof the first and second tunnels through these openings. An fastener 1558a is also inserted through the opening in V1, and into the tunnel ofvertebra V1 to secure end 1554 a to vertebra V1. Similarly, an fastener1558 b is inserted through the opening in V3, and into the tunnel ofvertebra V3 to secure end 1554 b to vertebra V3. Fasteners 1558 a, 1558b are illustrated as threaded interference screws that are embedded intovertebral bodies V1 and V3 so that they do not protrude from theposterior faces of vertebrae V1 and V2. However, other fasteners andfastening techniques described herein could also be employed withimplant 1354.

In one embodiment, the fasteners 1558 a, 1558 b can be oriented at anangle, alpha, with respect to the axial plane of the spinal column, inorder to provide a smooth transition for implant 1554 as it enters theopenings of the vertebrae V1 and V3. This reduces stress concentrationsat the junction between the implant 1554 and the vertebrae. In oneembodiment, angle, alpha, is about 45 degrees. Other embodimentscontemplate angular orientations that range from 0 degrees to about 80degrees and from about 25 degrees to 65 degrees.

The ends of implant 1554 and other possible implants can be providedwith pigtails or other extensions of reduced size for insertion throughthe openings and tunnels formed in the vertebrae. It is alsocontemplated that the ends of the implant can include eyelets, holes,loops or other configuration suitable for engagement with an anchor. Inanother embodiment, not shown in the FIGURE, the implant 1554 maycomprise a broad swath of material through which the fasteners 1558 arethreaded to provide attachment to the underlying vertebrae.

In FIG. 55, two stabilization devices 1550 are shown extending acrossthree vertebrae. It is further contemplated that more or fewerstabilization devices 1550 may be applied to a spine in parallel, andmay extend across more or fewer vertebrae.

While the implants 1554 do not provide stress shielding againstcompressive loading, they do provide stabilization by resistingextension, lateral bending, and rotation. Thus, this stabilizationdevice provides some stabilization while preserving motion between thevertebrae. Further details of structures that provide support andstability while preserving motion may be found in U.S. patentapplication Ser. No. 10/078,522 filed on Feb. 19, 2002, published asU.S. Patent Publication No. 2002/0120269 on Aug. 29, 2002, and U.S.patent application Ser. No. 10/083,199 filed on Feb. 26, 2002, publishedas U.S. Patent Publication No. 2002/0120270 on Aug. 29, 2002, which arehereby incorporated by reference in their entirety.

III. Further Methods of Applying a Stabilization Device

FIGS. 56-59 illustrate further methods of applying various types ofmotion preserving stabilization devices through an access device. Theterm “access device” is used in its ordinary sense (i.e. a device thatcan provide access) and is a broad term and it includes structureshaving an elongated dimension and defining a passage, e.g., a cannula ora conduit. These and similar methods also can be used to deliver anysuitable stabilization device, including those hereinbefore described.Also, some aspects of these methods may be similar to or combinable withthe methods described above in connection with the application of singleor multi-level fixation devices.

FIG. 56 shows that in one method, an access device 1704 is advancedthrough an incision 1708 in the skin and is further advanced to asurgical location adjacent the spine of the patient. The term “surgicallocation” is used in its ordinary sense (i.e. a location where asurgical procedure is performed) and is a broad term and it includeslocations subject to or affected by a surgery. The term “spinallocation” is used in its ordinary sense (i.e. a location associated witha spine) and is a broad term and it includes locations near a spine thatare sites for surgical spinal procedures. The access device 1704 may beadvanced generally posteriorly. The terms “posterior” and “posteriorly”are used in their ordinary sense (i.e., from or through the rear-facingside of the patient) and are broad terms and they include an approachalong any line generally behind and between the two lateral sides of thepatient. In the illustrated embodiment, the access device 1704 isadvanced along a generally postero-lateral approach and is positionedabove a portion of the spine. In one application, the access device 1704is positioned above at least one pedicular area of at least one of twoadjacent vertebrae. In another application, the access device 1704 maybe positioned above one or more pedicular areas of more than twoadjacent vertebrae.

The access device 1704 may be similar to those described above, e.g.,the expandable conduit 20, except as set forth below. The access device1704 preferably has an elongate body 1710 that extends between aproximal end 1712 and a distal end 1716. The elongate body 1710 has alength between the proximal end 1712 and the distal end 1716 that isselected such that when the access device 1704 is applied to a patientduring a surgical procedure, e.g., as shown in FIGS. 56-59, the distalend 1716 can be positioned inside the patient adjacent a spinallocation. When so positioned, the selected length of the elongate body1710 is such that the proximal end 1712 is located outside the patientat a suitable height.

In one embodiment, the elongate body 1710 comprises a proximal portion1720 and a distal portion 1724. The proximal portion 1720 may have agenerally oblong, oval, circular, or other suitable shape. The term“oblong” is used in its ordinary sense (i.e. having an elongated form)and is a broad term and it includes a structure having a dimension,especially one of two perpendicular dimensions, such as, for example,width or length, that is greater than another. The term “oval” is usedin its ordinary sense (i.e., egg like or elliptical) and is a broad termand includes oblong shapes having curved portions and oblong shapeshaving parallel sides and curved portions. The access device 1704 mayfurther have a circular cross-section near the proximal end 1712, nearthe distal end 1716, at the proximal and distal ends 1712, 1716, andfrom the proximal end 1712 to the distal end 1716. As discussed above,in another embodiment, the access device 1704 has an oblongcross-sectional shape in the proximal portion 1720. In particular, theaccess device 1704 may have an oblong cross-section near the proximalend 1712, near the distal end 1716, at the proximal and distal ends1712, 1716, and from the proximal end 1712 to the distal end 1716.

The access device 1704 preferably is capable of having a firstconfiguration for insertion to the surgical location over the twovertebrae, which may be a relatively low-profile configuration, and asecond configuration wherein increased access is provided to thesurgical space. In the second configuration, the distal end 1716 mayhave a cross-sectional area that is larger than that of the firstconfiguration at the distal end 1716. The distal portion 1724 of theaccess device 1704 may be expanded from the first configuration to thesecond configuration using an expander apparatus, such as the expanderapparatus 200, as discussed above in connection with the skirt portion24. When so expanded, the distal portion 1724, at the distal end 1716,defines a surgical space that includes a portion of at least onevertebra, and preferably two adjacent vertebrae.

The proximal and distal portions 1720, 1724 preferably are pivotallycoupled to each other, as indicated by the arrows 1728 in FIG. 56. Thearrows 1728 indicate that the proximal portion 1720 may be pivotedmedially and laterally with respect to the distal portion 1724. Thispivotal motion tends to expose to a greater extent medial and lateralportions of the surgical space defined within the perimeter of thedistal end 1716 of the access device 1704. In particular, pivoting theproximal portion 1720 laterally with respect to the distal portion 1724exposes a portion of one or more vertebrae (or a portion of an externalsurface of an annulus A of an intervertebral disc) generally closer tothe midline of the spine. Similarly, pivoting the proximal portion 1720medially with respect to the distal portion 1724 exposes a portion ofone or more vertebrae (or a portion of an external surface of theannulus A) generally closer to the transverse processes of thevertebrae.

In a like manner, as discussed further below, pivotal motion can beprovided in the cephalad-caudal direction to expose generally cephalador generally caudal peripheral portions of the surgical space definedwithin the perimeter of the distal end 1716.

At least one passage 1730 extends through the elongate body 1710 betweenthe proximal end 1712 and the distal end 1716. The passage 1730 providesvisualization of the surgical space in any suitable manner, e.g., by aviewing element, as discussed above. The passage 1730 also can providesufficient access to the surgical space, e.g., adjacent the spine, suchthat components of a wide variety of dynamic stabilization systems, aswell as implements adapted to deliver and apply such components, may bepassed therethrough to the surgical location.

As discussed above, in the method illustrated by FIG. 56, the distal end1716 of the access device 1704 may be inserted postero-laterally, to asurgical location adjacent to at least one vertebra and preferablyadjacent to the first vertebra V₁ and the second vertebra V₂ (See FIG.57). Insertion of the access device 1704 may be facilitated by firstdelivering a series of dilators, as discussed above in connection withthe expandable conduit 20. In one application, as discussed above, afterthe access device 1704 has been delivered, it can be expanded to thesecond configuration, as indicated schematically in FIG. 56. Furtherdetails of various additional embodiments of the access device 1704 maybe found in U.S. patent application Ser. No. 10/678,744, filed Oct. 2,2003, entitled MINIMALLY INVASIVE ACCESS DEVICE AND METHOD, published asU.S. Patent Application No. 2005/0075540 on Apr. 7, 2005, which ishereby incorporated by reference herein in its entirety.

After the access device 1704 is delivered, a stabilization device 1740is applied to the patient. In one embodiment, the stabilization device1740 is configured to stabilize at least two adjacent vertebrae whilepreserving a degree of motion. The term “dynamic stabilization” is usedin its ordinary sense (i.e., stabilizing adjacent vertebrae whilepermitting some degree of motion) and is a broad term and it includesstabilization that allows movement on a macroscopic or a microscopiclevel between adjacent vertebrae. The term “motion preserving” or“motion preservation” are used in their ordinary senses (i.e.,maintaining the ability for motion or movement) and is a broad term andit includes restoring at least some motion that had been lost due tospinal conditions. In one embodiment, the stabilization device 1740includes a fastener, e.g., a bone anchor 1744, to be secured to eachvertebrae V₁, V₂ and a connecting element 1748 configured to couple withthe bone anchors 1744 and to extend between the adjacent vertebrae andto preserve motion of the adjacent vertebrae with respect to each other.The bone anchor 1744 may be a screw that is similar to a standardpedicle screw or may be similar to the fastener 600. In one embodiment,the bone anchor 1744 has an elongate body 1752 that extends between aproximal end 1756 and a distal end 1760. The distal end 1760 preferablyis configured to engage bone, e.g., a vertebrae, in a suitable manner.In one embodiment, threads extend proximally from the distal end 1760.The proximal end 1756 of the bone anchor 1744 is configured to reside asuitable height above a vertebra when the bone anchor 1744 is appliedthereto and to couple with the connecting element 1748 in a suitablemanner, e.g., in a manner similar to the coupling between the elongatedmember 650 and the fastener 600.

The stabilization device 1740 is configured to allow movement, on amacroscopic or a microscopic level, between adjacent vertebrae to whichit is applied. In one embodiment, the connecting element 1748 isconfigured such that motion is permitted at the point at which theconnecting element 1748 is coupled with the bone anchor 1744 (See FIG.38). In another embodiment, the connecting element 1748 is configuredsuch that movement is allowed at a location between two adjacent boneanchors 1744 applied to two adjacent vertebrae (See FIG. 42).

In one application, the bone anchor 1744 is advanced through theproximal end 1712 of the access device 1704, through the passage 1730,and to the surgical location defined by the distal portion 1724 of theaccess device 1704. Thereafter, the bone anchor 1744 is advanced into aportion of a bone, e.g., into a pedicle of a vertebra which is to bedynamically stabilized.

Prior to insertion of the stabilization device 1740, surgical tools maybe delivered through the access device 1704 to prepare the vertebrae V₁,V₂ to receive the bone anchors 1744. In various methods, bone probes,taps, or sounders may be inserted through the access device 1704 inorder to perform procedures, e.g., drill and tap holes in the pediclestructures. Sounders may be used to assess the integrity of the portionof the vertebra or other bone where the bone anchor 1744 is to beapplied. Bone probes may be used to make the initial invasion into thebone. Taps may be used to thread a hole or to create a threaded hole inthe bone into which a bone anchor 1744 may be advanced. Any other usefulinstruments or preparatory procedures known to those skilled in the artmay also be used in various applications. These instruments preferablyhave lengths chosen such that when they are inserted through the accessdevice 1704 to the surgical space, their proximal ends extend proximallyof the proximal end 1712 of the access device 1704. This arrangementpermits the surgeon to manipulate these instruments proximally of theaccess device 1704.

The bone anchor 1744 may be advanced by any suitable implant insertiontool, e.g., a bone anchor insertion tool 1780. In one embodiment, thebone anchor insertion tool 1780 is an elongate body 1784 that extendsfrom a proximal end (not shown) configured to be grasped, e.g., manuallyby the surgeon, to a distal end 1788 and defines a length therebetween.The length of the elongate body 1784 is selected such that when the boneanchor insertion tool 1780 is inserted through the access device 1704 tothe surgical space, the proximal end extends proximally of the proximalend 1712 of the access device 1704. This arrangement permits the surgeonto manipulate the bone anchor insertion tool 1780 proximally of theaccess device 1704.

The distal end 1788 is configured to engage the proximal end 1756 of thebone anchor 1744. For example, the distal end 1788 may have a cavity1792 shaped to receive the proximal end 1756 of the bone anchor 1744. Inone embodiment, the cavity 1792 engages the proximal end 1756 of thebone anchor 1744 in a manner to enable the bone anchor 1744 to beadvanced, e.g., by transferring torsion applied to the proximal end ofthe bone anchor tool 1780 to the bone anchor 1744, into the pedicle orother bone segment. In another embodiment, the bone anchor insertiontool 1780 has a grip portion configured to engage the bone anchor 1744.In one embodiment, both the grip portion and the bone anchor 1744 arehexagonal and are configured such that the width of the proximal end ofthe bone anchor 1744 is slightly less than the width of the gripportion. Other means of coupling the bone anchor insertion tool 1780 tothe bone anchor 1744 that permit the bone anchor 1744 to be insertedthrough the access device 1704 could also be used.

As discussed above, in one embodiment, the access device 1704 providespivotal motion between the proximal and distal portions 1720, 1724, asindicated by the arrows 1728. This pivotal motion enables the boneanchor 1744 to be applied within a range of angles with respect to themid-plane of the spine. This enables the surgeon to select a preferredorientation of the bone anchor 1744 with respect to the vertebrae orother bone segment.

After the desired orientation of the bone anchor 1744 has been selectedand the bone anchor 1744 has been advanced into the vertebra, asindicated in FIG. 56, the bone anchor insertion tool 1780 may bedisengaged from the proximal end 1766 of the bone anchor 1744 andwithdrawn from the access device 1704, as indicated by the arrow 1796.

FIG. 57 shows that in one application, the access device 1704 isconfigured to extend between two adjacent vertebrae V₁, V₂ and toprovide access to at least a portion of a pedicle of each of thevertebrae V₁, V₂ at the same time. In this manner, a first bone anchor1744 a may be applied to the first vertebra V₁ and a second bone anchor1744 b may be applied to the second vertebra V₂ (which may be superioror inferior to the first vertebra V₁) without the need to repeat thesteps of inserting the access device 1704 over each vertebra to provideaccess to the pedicles thereof. Two separate access devices may be usedto access the pedicles of adjacent vertebrae or one access device may beinserted twice, once over each of the adjacent vertebra. Furthervariations and combination are also possible, e.g., one or two accessdevice may be applied on each side of the mid-line of the spine toaccess three adjacent vertebrae so that a multi-level dynamicstabilization device may be applied to couple three adjacent vertebrae.These procedures may be repeated on each side of the mid-line of thespine to apply multi-level dynamic stabilization devices on each sidethereof.

An arrow 1794 in FIG. 57 indicates that the proximal portion 1720 may bepivoted with respect to the distal portion 1724 to provide access to theperipheral regions of the surgical space defined by the distal end 1712of the access device 1704. This arrangement may simplify or facilitatethe insertion of the bone anchors 1744 a, 1744 b.

Once the bone anchors 1744 a, 1744 b are applied to the patient, theconnecting element 1748 may be advanced into the proximal end 1712 ofthe access device 1704, through the passage 1730, to the surgicallocation. Once at the surgical location, the connecting element 1748 maybe coupled with the bone anchors 1744 a, 1744 b in a suitable manner. Asdiscussed above, one arrangement preserves motion of the vertebrae V₁,V₂ by permitting movement at or near the coupling of one or both of theconnecting element 1748 and the bone anchors 1744. Another arrangementpreserves motion of the vertebrae V₁, V₂ by permitting movement at alocation between the bone anchors 1744 a, 1744 b. Another arrangementpreserves motion of the vertebrae V₁, V₂ by permitting movement both ator near the connecting element/bone anchor coupling(s) and at a locationbetween the bone anchors 1744 a, 1744 b.

In one embodiment, the connecting element 1748 is a flexible member thatpermits a degree of motion between the vertebrae V₁, V₂. FIG. 58 showsanother embodiment of a connecting element 1798 that is a dynamicconnecting element, e.g., an element that is configured such thatmovement is allowed at a location along the connecting element 1798 at alocation between two adjacent bone anchors 1744 applied to two adjacentvertebrae (See FIG. 42). In one embodiment, the connecting element 1798has a first member 1800 coupled with the first bone anchor 1744 a, andthereby with the first vertebra V₁, and a second member 1804 coupledwith the second bone anchor 1744 b, and thereby coupled with the secondvertebra V₂. The first and second members 1800, 1804 may be rigidmembers or they may be flexible. The first member 1800 has a first end1808 configured to couple with the first bone anchor 1744 a and a secondend with a chamber 1812 formed therein. The second member 1804 has afirst end 1816 configured to couple with the second bone anchor 1744 band a second end with a piston 1820 arranged thereon. When theconnecting element 1798 is assembled, the piston 1820 is arranged tomove within the chamber 1812, providing motion indicated by an arrow1824. The coupling of the piston 1820 and the chamber 1812 could alsopermit rotational motion of the first and second members 1800, 1804 asindicated by arrows 1828. The piston and chamber arrangement could beconfigured to permit a degree of pivoting of the first member 1800 withrespect to the second member 1804, as indicated by an arrow 1832. Otherarrangements of connecting elements could employ spring mechanisms,ball-and-socket joints, or any of the other geometries or arrangementsdescribed hereinabove.

The access device 1704 is advantageously configured to permit theforegoing steps to be performed in any order. For example, theconnecting elements 1748, 1798 may be advanced to the surgical locationbefore or after the first bone anchor 1744 a is applied to the firstvertebra V₁. In a like manner, the connecting elements 1748, 1798 may beadvanced to the surgical location before the second bone anchor 1744 bis applied to the second vertebra V₂. The connecting element 1748, 1798may further be coupled with the first bone anchor 1744 a before thesecond bone anchor 1744 b is applied to the second vertebra V₂. Otherorders of the foregoing steps are also possible.

In one procedure, once the bone anchors 1744 have been attached to thetwo adjacent vertebrae V₁, V₂, the connecting element 1748, 1798 may bedelivered through the access device 1704 to couple with the bone anchors1744. To facilitate insertion, a gripping apparatus, such as, e.g., theguide apparatus 800 described above, may be used to engage theconnecting element 1748, 1798 and manipulate it through the accessdevice 1704 to the surgical space. The connecting elements 1748, 1798may take many forms depending on the particular stabilization devicebeing delivered and the combination of vertebrae being treated.

In one embodiment, shown in FIG. 57, the connecting element 1748 is aflexible member, such as that described above for stabilization device1400. In another embodiment, shown in FIG. 58, the connecting element1798 may comprise a jointed link rod, such as that described above forstabilization device 1450.

Once the connecting element 1748, 1798 is appropriately seated on ornear the bone anchors 1744, clamping elements may be inserted throughthe access device 1704 in a manner similar to that described above. Theclamping elements may then be threadably or otherwise engaged with thebone anchors 1744, fixing the connecting element 1748, 1798 between theclamping element and the bone anchors 1744.

In some applications, a second access device, such as an expandableconduit 20 or other suitable access device, may be inserted into thepatient. For example, a second access device could be inserted through apostero-lateral approach on the contralateral side of the spine, e.g.,the opposite side of the spine across the mid-line of the spine, asindicated by an arrow 1836, to provide access to at least one of two ormore adjacent vertebrae. In another embodiment, a second access devicemay be inserted through an alternative approach on the same or oppositeside of the spine to provide access to at least one of two or moreadjacent vertebrae. This second access device may provide access to thevertebrae at about the same time as the first access device 1704 orduring a later or earlier portion of a procedure. In one method, twostabilization devices are inserted from both sides of the spine usingfirst and second access devices. Any combination of single, multiplestabilization devices, or stabilization device sub-components may bedelivered through one or more access devices from any combination of oneor more approaches, such as the approaches shown in FIGS. 56-59, or anyother suitable approach.

FIG. 59 shows schematically another form of a dynamic stabilizationtreatment that could be provided through the access device 1704. In thistreatment, one or more facet joints are removed and one or moreartificial facet joints are inserted in their place. As above, theaccess device 1704 is delivered to the surgical location and isconfigured to provide access to a surgical location.

The facet joint may be removed using any suitable technique. Preferably,the facet joint is removed by inserting one or more implements to thesurgical location through the access device 1704 and withdrawing facetjoint fragments from the surgical location through the access device1704.

After the facet joint is removed, a facet joint insertion tool 1860 maybe advanced into the access device 1704 and may be advanced through thepassage 1730 to a location adjacent where the natural facet joint hadbeen.

The facet joint insertion tool 1860 preferably has an elongate body witha proximal end (not shown) that is configured to be manipulated by asurgeon and a distal end 1864 that is configured to selectively engagean artificial facet joint configured to preserve motion of the vertebraeforming the face joint. One such artificial face joint is thereplacement facet joint 1868. Preferably the distal end 1864 includes areleasable clamp 1872 or other means for engaging the facet joint. Inone embodiment, the clamp 1872 is releasable at the proximal end of thefacet joint insertion tool.

The replacement facet joint 1868 preferably includes a generallysuperior member 1876, a generally inferior member 1880, and a connectingmember 1884 that is positioned between the superior member 1876 and theinferior member 1880. The superior member 1876 is configured to engagethe generally superior aspect of the facet portion of the vertebra V₁.The inferior member 1880 is configured to engage the generally inferioraspect of the facet portion of the vertebra V₂. In one embodiment, bonegrowth features are provided on the surfaces of the superior andinferior members 1876, 1880 that are intended to engage the vertebralsurfaces facing the facet joint. Although the bone growth features areshown as spikes in the illustrated embodiment, they may take any othersuitable form. The connecting member 1884 is a deformable member in oneembodiment that permits movement of the facets of the vertebrae V₁, V₂with respect to each other to provide dynamic stabilization of thevertebrae V₁, V₂.

FIG. 59 illustrates at least two stages of a method for implantingreplacement facet joint by way of the access device 1704 to providedynamic stabilization. In one stage, when the replacement facet joint1868 has been advanced to the surgical location, the facet jointinsertion tool 1860 is caused to release the replacement facet joint1868. This stage is represented by the schematic depiction of thereplacement facet joint 1868 located between the distal end of the facetjoint insertion tool 1860 and the vertebrae V₁, V₂. In another stage,the replacement facet joint 1868 is coupled with the adjacent vertebraeV₁, V₂ to form a replacement joint, as shown by the dashed outline of areplacement facet joint in positioned where the natural facet joint hadbeen.

The proximal portion 1720 of the access device 1704 is pivotal withrespect to the distal portion 1724 thereof, as illustrated by the dashedline representation of the proximal portion 1720 and the arrow 1794, asdiscussed above. This may facilitate one or more of the foregoing stepsof facet joint replacement dynamic stabilization.

Although the forgoing procedures are described in connection with asingle level postero-lateral procedure, other procedures are possible.For example, multiple level stabilization could be performed with theexpandable conduit 20 or other suitable access device as described abovewith reference to FIGS. 30-37. As discussed above, other applicationsare also possible in which the access device 1704 is not expanded priorto delivery of the stabilization device 1700. In such applications, theaccess device 1704 remains in the first configuration while some, all,or any of the steps described above are performed. Also, a motionpreserving stabilization procedure could be combined with various spinalprocedures used to partially fuse or rigidly fix adjacent vertebrae forstabilization along any suitable approach, e.g., anterior, lateral,posterior, transforaminal.

Although the methods discussed above are particularly directed to theinsertion of a stabilization device, the access device 1704 may also beused advantageously to extract or remove the stabilization device. Thesurgical tools also may be further configured to facilitate removal aswell as insertion. In one application, a motion preserving stabilizationdevice may be replaced with a generally inflexible stabilization device,such as those described above, through the access device 1704. Inanother application, a previously inserted generally inflexiblestabilization device may be replaced with a motion preservingstabilization device, such as those described above, through the accessdevice 1704.

The foregoing methods and apparatuses advantageously provide minimallyinvasive treatment of a person's spine in a manner that preserves somedegree of motion between the vertebrae. Accordingly, trauma to thepatient may be reduced thereby, and recovery time shortened. Asdiscussed above, the stabilization devices described herein provide amore normal post-recovery range of motion of the spine, which can reducethe need for additional procedures.

It will be understood that the foregoing is only illustrative of theprinciples of the invention, and that various modifications,alterations, combinations, and equivalents can be made by those skilledin the art without departing from the scope and spirit of the invention.

1. A stabilization system for a spinal column, the stabilization systemcomprising: a first vertebral fastener configured to be engaged with afirst vertebra, the first vertebral fastener including a housing and athreaded shank extending from the housing, the housing of the firstvertebral fastener including a channel extending from a first side ofthe housing to a second side of the housing; a second vertebral fastenerconfigured to be engaged with a second vertebra, the second vertebralfastener including a housing and a threaded shank extending from thehousing, the housing of the second vertebral fastener including achannel extending from a first side of the housing to a second side ofthe housing; a longitudinal member having a first end and a second end,the longitudinal member configured to extend between the housing of thefirst vertebral fastener and the housing of the second vertebralfastener; the longitudinal member comprising a plurality of thin sheetsconfigured to slide relative to one another to impart a degree oflateral flexibility on the longitudinal member; a first clamping deviceconfigured to engage the housing of the first vertebral fastener tofasten the longitudinal member in the channel of the housing of thefirst vertebral fastener; and a second clamping device configured toengage the housing of the second vertebral fastener to fasten thelongitudinal member in the channel of the housing of the secondvertebral fastener.
 2. The stabilization system of claim 1, wherein theplurality of thin sheets are mechanically coupled together proximate thefirst end of the longitudinal member to limit relative motion betweenthe plurality of thin sheets proximate the first end of the longitudinalmember.
 3. The stabilization system of claim 1, wherein the firstclamping device secures the longitudinal member in the channel of thehousing of the first vertebral fastener such that at least some of theplurality of thin sheets are permitted to slide relative to each other.4. The stabilization system of claim 3, wherein the second clampingdevice secures the longitudinal member in the channel of the housing ofthe second vertebral fastener.
 5. The stabilization system of claim 3,wherein the second clamping device clamps the longitudinal member in thechannel of the housing of the second vertebral fastener to rigidlyconnect a portion of the longitudinal member to the housing of thesecond vertebral fastener.
 6. The stabilization system of claim 1,wherein a first thin sheet of the plurality of thin sheets comprises afirst material and a second thin sheet of the plurality of thin sheetscomprises a second material different from the first material.
 7. Thestabilization system of claim 6, wherein the first material issubstantially incompressible along a longitudinal axis of thelongitudinal member.
 8. The stabilization system of claim 7, wherein thesecond material comprises a low-friction material.
 9. The stabilizationsystem of claim 1, wherein at least a portion of the plurality of sheetsis coated with a low-friction material.
 10. The stabilization system ofclaim 1, wherein the second clamping device includes an interlockingfeature interlocking with an interlocking feature of the longitudinalmember when the second clamping device is engaged with the housing ofthe second vertebral fastener while allowing the plurality of thinsheets to slide relative to each other and relative to the housing ofthe second vertebral fastener.
 11. A stabilization system for a spinalcolumn, the stabilization system comprising: a first vertebral fastenerconfigured to be engaged with a first vertebra, the first vertebralfastener including a housing and a threaded shank extending from thehousing, the housing of the first vertebral fastener including a channelextending from a first side of the housing to a second side of thehousing; a second vertebral fastener configured to be engaged with asecond vertebra, the second vertebral fastener including a housing and athreaded shank extending from the housing, the housing of the secondvertebral fastener including a channel extending from a first side ofthe housing to a second side of the housing; a longitudinal memberhaving a first end and a second end, the longitudinal member configuredto extend between the housing of the first vertebral fastener and thehousing of the second vertebral fastener; the longitudinal membercomprising a plurality of elongated load-bearing elements arranged in anarray, the array of elongated load-bearing element configured to resistaxial elongation and compression of the longitudinal member whileallowing lateral flexing of the longitudinal member when subjected tospinal loads; a first clamping device configured to engage the housingof the first vertebral fastener to fasten the longitudinal member in thechannel of the housing of the first vertebral fastener; and a secondclamping device configured to engage the housing of the second vertebralfastener to fasten the longitudinal member in the channel of the housingof the second vertebral fastener.
 12. The apparatus of claim 11, whereinthe array of elongated load-bearing elements comprises a linear array.13. The apparatus of claim 11, wherein the elongated load-bearingelements comprise sheets.
 14. The apparatus of claim 13, wherein thesheets are stacked adjacent one another.
 15. The apparatus of claim 14,wherein the sheets are moveable relative to one another in alongitudinal direction.
 16. The apparatus of claim 11, wherein the arrayof elongated load-bearing elements comprises a cylindrical array. 17.The apparatus of claim 11, wherein the elongated load-bearing elementscomprise axial rods.
 18. The apparatus of claim 17, wherein the axialrods are arranged in a cylindrical array around a core element of thelongitudinal member.